Method and system for detecting defects

ABSTRACT

System for scanning a surface, comprising a light source producing an illuminating light beam; an objective lens assembly, located between the light source and the surface; a plurality of interchangeable telescopes, a selected one of the interchangeable telescopes being located between the light source and the objective lens assembly; and at least one light detector, wherein at least one of the light detectors detects at least a portion of a reflected light beam, reflected from the surface and received from the selected telescope.

FIELD OF THE DISCLOSED TECHNIQUE

[0001] The disclosed technique relates to systems and methods fordetecting defects and anomalies in surfaces, in general and to systemsand methods for detecting defects and anomalies in silicon wafer used inthe production of semiconductor devices, in particular.

BACKGROUND OF THE DISCLOSED TECHNIQUE

[0002] A silicon wafer is etched by using different photographic masksto produce large-scale integrated (LSI) semiconductor circuits,very-large-scale integrated (VLSI) semiconductor circuits or ultra-largescale integrated (ULSI) semiconductor circuits. In general, aphotographic mask is imprinted with a predetermined pattern. The patternis then imprinted on the wafer by various lithographic methods. It shallbe appreciated by those skilled in the art that the pattern imprinted onthe wafer should be essentially identical to the predetermined pattern.Any deviation from the predetermined pattern would constitute a defectand shall render that wafer defective. Also, any imperfection on thenon-etched surface of the silicon wafer (such as pits, scratches,foreign matter particles etc.) may also constitute an undesirabledefect.

[0003] Hence, it is important to detect such defects. When a defect isdetected, either at least a portion of the wafer is discarded or thedefect is analyzed to determine if it constitutes a critical defect or anuisance defect (a defect which will not adversely affect performance).Therefore it is important that the inspection system does not declare“false defects” (i.e., declare a defect for a non-defective wafer).

[0004] Semiconductor circuits are becoming more and more complex,condensed in structure and smaller in size, and are thus more prone todefects. A conventional method for detecting defects often includesseveral different test procedures.

[0005] Conventional optical inspection system, utilize bright-field,dark-field and gray-field detection based techniques. Bright-field,dark-field and gray-field based techniques, are generally defined asimaging techniques wherein the detected image is completely bright,completely dark, or partially bright, respectively, in the absence of aspecimen.

[0006] In a simple bright-field based technique, an illumination systemilluminates a specimen from above, and a collection optical systemlocated above or below the specimen, detects the light reflected orscattered from the specimen. The broadest definition of bright-fieldlight refers to light thus collected. It is noted, however, that othertechniques use different definitions of a bright-field light beam, asshall be described herein below.

[0007] In a typical dark-field based technique, either the specimen isilluminated from above and light reflected there from is collected fromthe sides, or the specimen is illuminated from the side and lightreflected there from is collected from above. The light thus collectedis typically referred to as the dark-field light beam. A typicalgray-field based technique shall be discussed herein below withreference to FIG. 1.

[0008] U.S. Pat. No. 6,178,257 entitled “Substrate Inspection Method andApparatus”, U.S. Pat. No. 5,699,447 entitled “Two-Phase OpticalInspection Method and Apparatus for Defect Detection”, and U.S. Pat. No.5,982,921 entitled “Optical inspection method and apparatus”, all issuedto Alumot et al. and assigned to the assignee of the present disclosedtechnique, describe a dark-field detection system, and are incorporatedherein by reference. U.S. Pat. No. 6,122,046 issued to Almogy et al.,entitled “Dual Resolution Combined Laser Spot Scanning and Area ImagingInspection”, and assigned to the assignee of the present disclosedtechnique, describes a detection system utilizing a technique combiningdark-field and bright-field imaging, and is also incorporated herein byreference.

[0009] U.S. Pat. No. 6,259,093 issued to Wakiyama et al., entitled“Surface Analyzing Apparatus”, is directed to an apparatus for thedetection of foreign matter and defects on a wafer surface. A polarizedlaser light is scattered from the wafer surface and is detected in anoptical microscope. Since the pattern imprinted on the wafer causes aconstant polarization in the reflected light, an appropriate polarizingmask on the microscope side, reduces the intensity of the reflectedlight. However, the light reflected from surface defects and foreignmatter is significantly less influenced by the mask and hence does notexhibit a reduction in brightness, and is therefore detectable (i.e.,distinguished from the polarized light).

[0010] U.S. Pat. No. 5,699,447 issued to Alumot et al., entitled“Two-phase optical inspection method and apparatus for defectdetection”, is directed to a method for detecting defects on patternedwafers. The wafer is illuminated and light diffracted from the wafersurface is collected by a plurality of detectors, arranged in a circularpattern around the inspected wafer.

[0011] U.S. Pat. No. 6,064,517 issued to Chuang et al., entitled “HighNA System for Multiple Mode Imaging”, is directed to an inspectionapparatus which provides different imaging modes, such as dark-field andbright-field. The apparatus includes a high numerical aperturecatadioptric (using both reflection and refraction to form an image)optical group which forms an intermediate image, the image is thencorrected for aberrations by a focusing group and mapped to a planelocated at a pupil of the system. Apertures placed at this plane can beused to limit the range of scattering angles reaching the imagedetector.

[0012] U.S. Pat. No. 6,122,046 issued to Almogy et al., entitled “DualResolution Combined Laser Spot Scanning and Area Imaging Inspection”, isdirected to an apparatus for optically detecting defects in a siliconsubstrate. A linearly polarized light beam is passed through a beamsplitter, which is aligned so as to transmit the illuminating light beamwithout deflection. The illuminating light beam then passes through aquarter wave plate which circularly polarizes it. The illuminating lightbeam is then reflected from the inspected surface. The reflected lightpasses through the quarter wave plate in the opposite direction and islinearly polarized thereby, but in a direction perpendicular to theoriginal linear polarization direction of the illuminating light beam.The reflected light beam is deflected by the beam splitter, due to itsperpendicular polarization, toward a bright-field detector.

[0013] The article “Detection of Fibers by Light Diffraction”, J. Listet al. (1998), describes an apparatus for the detection of asbestosfibers in air flow. The device described detects light scattered fromthe fibers in the air. A pulsed Nd:YAG laser produces a high intensityilluminating light beam. An apertured mirror is located at the oppositeside of the laser source, admitting the illuminating light beam toward alight trap and deflecting light, scattered by the asbestos fibers in theair, toward a light detector (CCD). The apertured mirror protects thelight detector from the high intensity illuminating light beam.

[0014] Reference is now made to FIG. 1, which is a schematicillustration of a system, generally referenced 10, for scanning a wafersurface, which is known in the art. System 10 is used for scanning awafer surface 12. System 10 includes a laser light source 14, a scanner16, a polarizing beam splitter 20, a quarter wave plate 24, an objectivelens assembly 26, a relay lens assembly 32, an annular mirror 34, abright-field detector 36 and a gray-field detector 38.

[0015] Laser light source 14, scanner 16, polarizing beam splitter 20,quarter wave plate 24 and objective lens assembly 26 are positionedalong a first optical axis 60. Polarizing beam splitter 20, relay lensassembly 32, annular mirror 34 and bright-field detector 36 arepositioned along a second optical axis 62. Annular mirror 34 andgray-field detector 38 are positioned along a third optical axis 64.

[0016] Polarizing beam splitter 20 includes a semi-transparentreflection plane 22. Reflection plane 22 is oriented at 45 degreesrelative to wafer surface 12. Annular mirror 34 is oriented at 45degrees relative to optical axes 62 and 64. For purposes of simplicity,objective lens assembly 26 is depicted in 2A as a basic objective lensassembly, including an aperture stop 28, located at a pupil of thescanning system, and an objective lens 18. Objective lens 18 has a focallength F₁. Aperture stop 28 has a diameter D_(P).

[0017] Laser light source 14 emits a laser light beam 40, which is thenreceived by scanner 16. Scanner 16 expands and redirects laser lightbeam 40, thereby emitting alternating illuminating light beams atdynamically changing angles and a constant diameter D. The exampleillustrated in FIG. 1 shows only an illuminating light beam 44, having amaximal scanning angle θ, relative to optical axis 60. Otherilluminating light beams (not shown) have scanning angles between θ and−θ.

[0018] Illuminating light beam 44 passes through polarizing beamsplitter 20 and from there, further through quarter wave plate 24.Quarter wave plate 24 circularly polarizes illuminating light beam 44 ina first angular direction. Illuminating light beam 44 enters objectivelens assembly 26 and passes through aperture stop 28. Objective lensassembly 26 focuses illuminating light beam 44 onto a point 30 ₁ onwafer surface 12.

[0019] Illuminating light beam 44 is reflected and scattered from point30 ₁, in a plurality of directions. Some of the reflected and scatteredlight is collected by the objective lens assembly, and used to detectthe properties of wafer surface 12. According to this technique, thecollected light includes a bright-field light beam portion and agray-field light beam portion. The bright-field light beam is defined aslight the portion of collected light which follows the exact path of theilluminating light beam. The gray-field light beam is defined as therest of the collected light, which is not included in the bright-fieldlight beam. A bright-field light beam 50 and a gray-field light beam 52,of the light scattered and reflected from point 30 ₁, are collected byobjective lens 18. Objective lens 18 collimates bright-field light beam50 and gray-field light beam 52, and directs the light beams throughaperture stop 28.

[0020] Light beams 50 and 52 exit from objective lens assembly 26circularly polarized in the opposite angular direction as illuminatinglight beam 44. Light beams 50 and 52 pass through quarter wave plate 24,and become linearly polarized, perpendicular to the polarization ofilluminating light beam 44. Light beams 50 and 52 are then reflected offsemi-transparent reflection plane 22, and directed to relay lensassembly 32.

[0021] Relay lens assembly 32 produces an inverted image of the pupil ofaperture stop 28, at the pupil of annular mirror 34. Bright-field lightbeam 50 passes through the aperture of annular mirror 34. Bright-fielddetector 36 receives bright-field light beam 50 and detects theintensity thereof. Gray-field light beam 52 is reflected off annularmirror 34. Gray-field detector 38 receives gray-field light beam 52 anddetects the intensity thereof.

[0022] It is noted that the light beams emitted at other times andhaving other scanning angles, reach other points on wafer surface 12,between point 30, and another point 30 ₂, which is located on theopposite side of optical axis 60 from point 30 ₁.

[0023] System 10 further includes additional objective lens assemblies(not shown), which are interchangeable with objective lens assembly 26.These objective lens assemblies are mounted on a turret, a slide (bothnot shown), and the like, which enables interchanging objectives. Eachof the different objective lens assemblies is used for a different modeof operation.

[0024] Reference is further made to FIGS. 2A and 2B. FIG. 2A is aschematic illustration of objective lens assembly 26 and scanned wafersurface 12 of system 10 (FIG. 1). FIG. 2B is a schematic illustration ofan additional objective lens assembly 102 which replaces objective lensassembly 26 (FIG. 2A), and scanned wafer surface 12.

[0025] With reference to FIG. 2B, objective lens assembly 102 replacesobjective lens assembly 26 (FIG. 2A). It is noted that the opticalelements of objective lens assembly 102 are not shown. Objective lensassembly 102 has a focal length F₂ equal to ½F₁, wherein F₁ is the focallength of objective lens assembly 26 (FIG. 2A).

[0026] Objective lens assembly 102 receives an illuminating light beam110 ₁ of diameter D, and focuses it onto a point 120 ₁ on wafer surface12. Illuminating light beam 110 ₁ is similar to illuminating light beam44 (FIG. 2A), having a maximal scanning angle θ.

[0027] Objective lens assembly 102 collects a bright-field light beam110 ₁ having diameter D and a gray-field light-beam 112 ₁ havingdiameter D_(P). It is noted that objective lens assembly 102 may includevarious optical elements (e.g., lenses, stops, and the like), which arenot shown.

[0028] The line between points 30 ₁ and 30 ₂ (FIG. 2A) on wafer surface12, is known as the scan line of system 10. It is well known that thescan line length is proportional to the focal length of the objectivelens assembly. Hence, the scan line length for the system of FIG. 2B, isapproximately ½ of the scan line length of system of FIG. 2A.Furthermore, it is well known that the scanning speed of a scanningsystem such as system 10 (FIG. 1), is proportional to the square of thescan line length.

[0029] It is also well known that the numerical aperture of the scanninglight beams of system 10 is inversely proportional to the focal lengthof the objective lens assembly used. Hence, the numerical aperture forsystem of FIG. 2B, is approximately 2 times the numerical aperture forsystem of FIG. 2A. Furthermore, is well known that the scanningresolution for a scanning system such as system 10 is proportional tothe numerical aperture.

[0030] Thus, by selecting different objectives with different focallengths, the user of system 10 can choose between a low-speed,high-resolution and a high-speed, low-resolution scan. It is noted thatto increase the gray-field numerical aperture, it is required toincrease both the numerical aperture of the objective lens assembly andthe size of the polarizing beam splitter. The cost of an objective lensassembly and the cost of a polarizing beam splitter, are highlycorrelated with their respective sizes. Hence, increasing the gray-fieldnumerical aperture for system 10 involves a significant cost increase.It is still further noted that the objective lens assembly is theelement of system 10 which is closest to the wafer, located directlythere above. Hence, replacing objectives when changing magnificationmodes, involves a risk of contaminating the inspected wafer.

SUMMARY OF THE DISCLOSED TECHNIQUE

[0031] It is an object of the disclosed technique to provide a novelmethod and system for detecting defects in printed surfaces in generaland for detecting defects and anomalies in silicon wafer used in theproduction of semiconductor devices, which overcomes the disadvantagesof the prior art.

[0032] In accordance with the disclosed technique, there is thusprovided a system for scanning a surface including a light sourceproducing an illuminating light beam, an objective lens assembly,located between the light source and the surface, a plurality ofinterchangeable telescopes, wherein a selected one of theinterchangeable telescopes being located between the light source andthe objective lens assembly and a plurality of light detectors. At leastone of the light detectors detects at least a portion of a reflectedlight beam, received from the selected telescope.

[0033] In accordance with another aspect of the disclosed techniquethere is thus provided a system for scanning a surface, including alight source producing an illuminating light beam; an objective lensassembly, located between the light source and the surface; at least onelight detector; and an annular mirror located between the light sourceand the objective lens assembly. The annular mirror admits theilluminating light beam and deflects at least a portion of a reflectedlight beam received from the objective lens assembly, toward one of thelight detectors. An additional beam splitter can be added to this systembetween the light source and the annular mirror. In this case, the beamsplitter deflects the portion of the reflected light beam, which passesthrough the opening of the annular mirror, towards another lightdetector.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The disclosed technique will be understood and appreciated morefully from the following detailed description taken in conjunction withthe drawings in which:

[0035]FIG. 1 is a schematic illustration of a system for scanning awafer surface, which is known in the art;

[0036]FIG. 2A is a schematic illustration of the objective lens assemblyof the system of FIG. 1 and the scanned wafer surface;

[0037]FIG. 2B is a schematic illustration of an additional objectivelens assembly which replaces the objective lens assembly of FIG. 2A, andthe scanned wafer surface;

[0038]FIG. 3A is a schematic illustration of a system for scanning awafer surface, constructed and operative in accordance with anembodiment of the disclosed technique, at a first moment in time;

[0039]FIG. 3B is a schematic illustration of the system of FIG. 3A, atanother moment in time;

[0040]FIG. 3C is a schematic illustration of the system of FIGS. 3A and3B, including the light beams of both FIGS. 3A and 3B;

[0041]FIG. 4A is an illustration in detail of the aperture stop,telescope and objective lens assembly, of the system of FIG. 3A, at afirst moment in time;

[0042]FIG. 4B is an illustration of the elements presented in FIG. 4A,at a second moment in time;

[0043]FIG. 4C is an illustration of the elements presented in FIGS. 4Aand 4B, including the light beams of both FIGS. 4A and 4B;

[0044]FIG. 4D is an illustration in detail of the aperture stop andobjective lens assembly of system 200, another telescope replacing thetelescope of FIG. 4A and used in another mode of operation of the systemof FIG. 3A, and scanned wafer surface;

[0045]FIG. 4E is an illustration in detail of the aperture stop andobjective lens assembly of the system of FIG. 3A, a further telescope,replacing the telescope of FIG. 4a and used in a further mode ofoperation of the system of FIG. 3a, and scanned wafer surface;

[0046]FIG. 5 is a schematic illustration of a scanning systemconstructed and operative in accordance with another embodiment of thedisclosed technique;

[0047]FIG. 6 is a schematic illustration of a scanning system usingapodizators, constructed and operative in accordance with a furtherembodiment of the disclosed technique;

[0048]FIG. 7A is a schematic illustration of an apodizator constructedand operative in accordance with an embodiment of the disclosedtechnique;

[0049]FIG. 7B is a schematic illustration of the objective lens assemblyand the scanned wafer surface of FIG. 6, and an illuminating light beamwhich has already passed through the apodizator of FIG. 7A;

[0050]FIG. 7C is a schematic illustration of a bright-field light beamand a gray-field light beam, which are reflections and refractions ofilluminating light beam of FIG. 7B, by the wafer surface, traveling fromthe scanned wafer surface and passing through the objective lensassembly of the system of FIG. 6;

[0051]FIG. 8A is a schematic illustration of another apodizator,constructed and operative in accordance with another preferredembodiment of the disclosed technique;

[0052]FIG. 8B is a schematic illustration of the objective lens assemblyand the scanned wafer surface of FIG. 6, and an illuminating light beamwhich has already passed through the apodizator of FIG. 8A;

[0053]FIG. 8C is a schematic illustration of a bright-field light beamand a gray-field light beam, which are reflections and refractions ofilluminating of the illuminating light beam of FIG. 8B, by the wafersurface, traveling from the scanned wafer surface and passing throughthe objective lens assembly of the system of FIG. 6;

[0054]FIG. 9A is a schematic illustration of another apodizator,constructed and operative in accordance with a further embodiment of thedisclosed technique;

[0055]FIG. 9B is a schematic illustration of the objective lens assemblyand the scanned wafer surface of FIG. 6, and an illuminating light beamwhich has already passed through the apodizator of FIG. 9A;

[0056]FIG. 9C is a schematic illustration of a bright-field light beamand a gray-field light beam, which are reflections and refractions ofthe illuminating light beam of FIG. 9B, by the wafer surface, travelingfrom the scanned wafer surface and passing through the objective lensassembly of the system of FIG. 6;

[0057]FIG. 10A is a schematic illustration of another apodizator,constructed and operative in accordance with another embodiment of thedisclosed technique;

[0058]FIG. 10B is a schematic illustration of the objective lensassembly and the scanned wafer surface of FIG. 6, and an illuminatinglight beam which has already passed through the apodizator of FIG. 10A;

[0059]FIG. 10C is a schematic illustration of a bright-field light beamand a gray-field light beam, which are reflections and refractions ofthe illuminating light beam of FIG. 10B, by the wafer surface, travelingfrom the scanned wafer surface and passing through the objective lensassembly of the system of FIG. 6;

[0060]FIG. 11A is a schematic illustration of another apodizatorconstructed and operative in accordance with a further embodiment of thedisclosed technique;

[0061]FIG. 11B is a schematic illustration of the objective lensassembly and the scanned wafer surface of FIG. 6, and an illuminatinglight beam which has already passed through the apodizator of FIG. 11A;

[0062]FIG. 11C is a schematic illustration of a bright-field light beamand a gray-field light beam, which are reflections and refractions ofthe illuminating light beam of FIG. 11B, by the wafer surface, travelingfrom the scanned wafer surface and passing through the objective lensassembly of the system of FIG. 6;

[0063]FIG. 12 is a schematic illustration of a dynamic apodizator, and acontroller, constructed and operative in accordance with anotherembodiment of the disclosed technique;

[0064]FIG. 13A is a schematic illustration of a bright-field filter;

[0065]FIG. 13B is a schematic illustration of the bright-field filter ofFIG. 13A and a bright-field light beam incident there upon and partiallytransmitted there through;

[0066]FIG. 13C is a schematic illustration of the objective lensassembly of the system of FIG. 6, the scanned wafer surface, theilluminating light beam of FIG. 9A, and the bright-field light beam ofFIG. 13B and a gray field light beam, which are reflections andrefractions of the illuminating light beam from the wafer surface ofFIG. 6;

[0067]FIG. 14 is a schematic illustration of a system for scanning awafer surface, according to another embodiment of the disclosedtechnique;

[0068]FIG. 15 is a schematic illustration of a system for scanning awafer surface, according to a further embodiment of the disclosedtechnique;

[0069]FIG. 16 is a schematic illustration of a front end opticalassembly for scanning a wafer surface, according to another embodimentof the disclosed technique;

[0070]FIG. 17 is a schematic illustration of a method for operatingeither of the systems of FIGS. 14 and 15 or the front end assembly ofFIG. 16, operative in accordance with another embodiment of thedisclosed technique;

[0071]FIG. 18 is a schematic illustration of a multi-zone gray-fielddetector constructed and operative in accordance with a furtherembodiment of the disclosed technique;

[0072]FIG. 19 is a schematic illustration of a system for scanning awafer surface, constructed and operative in accordance with anotherembodiment of the disclosed technique; and

[0073]FIG. 20 is a schematic illustration of a method for inspecting asurface, in accordance with another embodiment of the disclosedtechnique.

DETAILED DESCRIPTION OF EMBODIMENTS

[0074] The disclosed technique overcomes the disadvantages of the priorart by providing a novel method and system for detecting defects insemiconductor manufacturing procedures, using interchangeable telescopesand a single objective.

[0075] In the following description the following terms are used:

[0076] Illuminating light beam—a light beam originating from a lightsource and illuminating an inspected object.

[0077] Illumination path—the path of the illuminating light beam.

[0078] Normally collected light beam—a light beam reflected or scatteredoff an inspected object and reaching an objective lens above theinspected object.

[0079] Collection path—the path of the collected light beam.

[0080] Combined path—the intersection of the illumination and collectionpaths.

[0081] Bright-field light beam—the portion of the normally collectedlight beam coinciding with the illumination path.

[0082] Gray-field light beam—the portion of the normally collected lightbeam not coinciding with the illumination path.

[0083] Pupil of a scanning system—a geometric location wherein all thescanning light beams coincide.

[0084] The disclosed technique has several aspects. According to oneaspect of the disclosed technique, interchangeable telescopes,positioned in the combined path, determine the modes of operation of thescanning system. According to another aspect of the disclosed technique,the combined bright-field and gray-field light beam arrives first at anannular mirror, which separates between the bright-field and thegray-field light beams. According to a further aspect of the disclosedtechnique, there is provided a novel optical structure for changing theshape of an illuminating light beam, without directly affecting theshape of the respective collected light beams. According to anotheraspect of the disclosed technique, the apodizators are combined withbright-field filters, which block a selected portion of the bright-fieldlight beam before the bright-field light beam reaches the bright-fielddetector. According to a further aspect of the disclosed technique,continuous range magnification replaces the discrete valuesmagnification which was provided by the interchangeable telescopes. Itis noted that various combinations of the above aspects may beimplemented in a single scanning system.

[0085] According to one embodiment of the disclosed technique, thescanning system illustrated in FIG. 1 is replaced by an alternativescanning system, such as the system illustrated below in FIGS. 3A and3B. Accordingly, the portion of the scanning system of FIG. 1, whichchanges according to the selected magnification mode, as illustrated indetail in FIGS. 2A and 2B, is replaced by the portion of the scanningsystem of FIGS. 3A and 3B, which changes according to the selectedmagnification mode, as illustrated in detail in FIGS. 4A, 4B and 4C.

[0086] Reference is now made to FIGS. 3A, 3B and 3C. FIG. 3A is aschematic illustration of a system, generally referenced 200, forscanning a wafer surface, constructed and operative in accordance withan embodiment of the disclosed technique, at a first moment in time.FIG. 3B is a schematic illustration of the system of FIG. 3A, at anothermoment in time. FIG. 3C is a schematic illustration of the system ofFIGS. 3A and 3B, including the light beams of both FIGS. 3A and 3B.

[0087] In the example set forth in FIGS. 3A, 3B and 3C system 200 isused for scanning a wafer surface 202. System 200 includes a laser lightsource 204, a scanner 206, a polarizing beam splitter 210, a quarterwave plate 214, an aperture stop 218, a telescope 216, an objective lensassembly 222, a relay lens assembly 230, a bright-field detector 234 anda gray-field detector 236.

[0088] Laser light source 204, scanner 206, polarizing beam splitter210, quarter wave plate 214, aperture stop 218, telescope 216, objectivelens assembly 222 and wafer surface 202 are positioned along a firstoptical axis 260. First optical axis 260 is perpendicular to wafersurface 202. Scanner 206 is positioned between laser light source 204and polarizing beam splitter 210. Quarter wave plate 214 is positionedbetween polarizing beam splitter 210 and aperture stop 218. Telescope216 is positioned between aperture stop 216 and objective lens assembly222. Objective lens assembly 222 is positioned between telescope 216 andwafer surface 202.

[0089] Polarizing beam splitter 210, relay lens assembly 230, annularmirror 232 and bright-field detector 234 are positioned along a secondoptical axis 262. In the present example, second optical axis 262 isperpendicular to first optical axis 260. Relay lens assembly 230 ispositioned between polarizing beam splitter 210 and annular mirror 232.Annular mirror 232 is positioned between relay lens assembly 230 andbright-field detector 234.

[0090] Annular mirror 232 and gray-field detector 236 are positionedalong a third optical axis 264. In the present example, third opticalaxis 264 is parallel to first optical axis 260.

[0091] Polarizing beam splitter 210 includes a semi-transparentreflection plane 212. Semi-transparent reflection plane 212 eithertransmits or reflects light incident thereupon, depending on the stateof polarization of the incident light. In the present example,semi-transparent reflection plane 212 is oriented at 45 degrees relativeto wafer surface 202. Quarter-wave plate 214 adds a π/2 phase (i.e., ¼of a cycle) to one of the linearly polarized components of lightincident there upon. It is noted that quarter-wave plate 214 andpolarizing beam splitter 210 may be incorporated in a single module.Annular mirror 232 is located at a pupil of the scanning system. Annularmirror 232 reflects light at all areas thereof (excluding the aperture).In the present example, annular mirror 232 is oriented at 45 degreesrelative to optical axes 262 and 264.

[0092] It is noted that the annular mirror, which is also known as theapertured mirror, may have various orientations and shapes. For example,the annular mirror may be elliptical, with an elliptical aperture.Accordingly, the inner and outer diameters of annular mirror 232, in thedirection perpendicular to the plane defined by optical axes 260 and262, are D_(IL) and D_(TP), respectively, wherein D_(TP) is the aperturediameter of aperture stop 218, and D_(IL) is the diameter of theilluminating light beams, as explained herein below. Furthermore, theinner and outer diameters of the mirror in the direction of optical axis264, may be set to at least •2×D_(IL) and •2×D_(TP), respectively, butgenerally depend also on θ_(IL), which is the scanning angle, asexplained herein below.

[0093] Bright-field detector 234 and gray-field detector 236 detectproperties of light incident there upon.

[0094] Reference is further made to FIGS. 4A, 4B and 4C. FIG. 4A is anillustration in detail of the aperture stop 218, telescope 216 andobjective lens assembly 222, of system 200, and scanned wafer surface202 (FIG. 3A), at a first moment in time. FIG. 4B is an illustration ofthe system of FIG. 4A, at a second moment in time. FIG. 4C is anillustration of the system of FIGS. 4A and 4B, including the light beamsof both FIGS. 4A and 4B.

[0095] Aperture stop 218 is located at the entrance pupil of telescope216. Aperture stop 218 includes an aperture of diameter D_(TS). Aperturestop 218 transmits incident light through the aperture, and rejects(i.e., reflects or absorbs) all other incident light. For example,aperture stop may be an annular non-transmitting disk of inner diameterD_(TS), and a substantially larger outer diameter (e.g., twice as largeas the inner diameter).

[0096] Telescope 216 includes a first telescope lens 266 and a secondtelescope lens 268. Telescope lenses 266 and 268 have equal focallengths. Objective lens assembly 222 includes an objective aperture stop224 and an objective lens 226. Objective aperture stop 224 is located atthe exit pupil of telescope 218, which is also the entrance pupil ofobjective lens assembly 222. Objective aperture stop 224 has an aperturediameter of D_(OS). In the present example, D_(TS)=D_(OS), whereinD_(TS) is the diameter of aperture stop 218. Objective lens 226 has afocal length F.

[0097] For purposes of simplicity, objective lens assembly 222 andtelescope 216 are depicted in FIGS 4A, 4B, and 4C as a basic objectivelens assembly and a basic telescope, respectively. It is noted, however,that system 200 may use a more complex objective lens assembly and amore complex telescope instead of objective lens assembly 222 andtelescope 216, respectively. Accordingly, the telescope and objectivelens assembly may include additional optical elements and may havedifferent dimensions from objective lens assembly 222 and telescope 216,respectively.

[0098] Referring back to FIGS. 3A, 3B and 3C, system 200 performs alinear scan of wafer surface 202 by illuminating points on a line onwafer surface 202, collecting the light reflected and scattered therefrom, and detecting scattered and reflected light. Laser light source204 emits a laser light beam 240 toward scanner 206. Scanner 206receives laser light beam 240. Scanner 206 expands and redirects laserlight beam 240, thereby producing alternating illuminating light beams244 ₁ and 244 ₂ each produced at a different time. Illuminating lightbeams 244 ₁ and 244 ₂ are collimated, and linearly polarized in a firstpredetermined direction of linear polarization. It is noted that for thepurpose of simplicity, all of the illuminating light beams mentionedherein, have a circular cross-section, unless otherwise stated.

[0099] At a first moment in time, scanner 206 emits illuminating lightbeam 244 ₁, at a diameter D_(IL) and an angle θ_(IL) relative to firstoptical axis 260. In the present example, D_(IL) is approximately equalto ¼D_(TS). At a second moment in time, scanner 206 emits illuminatinglight beam 244 ₂, also at diameter D_(IL) and angle θ_(IL) relative tofirst optical axis 260. Illuminating light beams 244 ₁ and 244 ₂ are onopposite sides of first optical axis 260. It is noted that theillumination angle θ_(IL), is generally small (i.e., θ_(IL)<10 degrees).Hence, small-angle approximations apply.

[0100] Illuminating light beam 244 ₁ passes through polarizing beamsplitter 210 and from there, further through quarter wave plate 214.Quarter wave plate 214 circularly polarizes illuminating light beam 244₁ in a first angular direction (e.g., clockwise). Illuminating lightbeam 244 ₁ then passes through aperture stop 218 and enters telescope216.

[0101] With reference to FIGS. 4A, 4B and 4C, telescope 216 produces aninverted image of the pupil of aperture stop 218, at the pupil ofobjective aperture stop 224, at a magnification ratio M=1. Telescope 216emits light beam 244 ₁ at a diameter D_(BF1), and an angle θ₁ relativeto first optical axis 260. In general, the angular magnification of atelescope is the reciprocal of the linear magnification of thetelescope. The angular magnification and the linear magnification oftelescope 216 are both equal to 1. Accordingly, in the present example,D_(BF1)=D_(IL), and θ₁=θ_(IL).

[0102] Illuminating light beam 244 ₁ enters objective lens assembly 222and passes through objective aperture stop 224. Objective lens assembly222 focuses illuminating light beam 244 ₁ onto a point 230 ₁ on wafersurface 202.

[0103] Wafer surface 202, depending on the properties of the variouselements thereon (e.g., topography, reflectivity, and the like),reflects and scatters illuminating light beam 244 ₁ from point 230 ₁ ina plurality of directions.

[0104] A bright-field light beam 250 ₁ and a gray-field light beam 252₁, of the scattered and reflected light, are received at objective lensassembly 222. Objective lens 226 collimates light beams 250 ₁ and 252 ₁.Objective lens 226 directs bright-field light beam 250 ₁ throughobjective aperture stop 224 at diameter D_(BF1). Objective lens 226directs gray-field light beam 252 ₁ to objective aperture stop 224 at anouter diameter D_(GF1) and inner diameter D_(BF1). It is noted that theouter diameter D_(GF1) of gray-field light beam 252 ₁ may generallydepend on both the diameter D_(OS) of objective aperture stop 224 andthe diameter D_(TS) of aperture stop 218. In the present example,D_(GF1) is equal to D_(OS) or, equivalently, to D_(TS).

[0105] Light beams 250 ₁ and 252 ₁ pass through objective aperture stop224 and enter telescope 216. Telescope 216 emits light beams 250 ₁ and252 ₁ toward aperture stop 218. Telescope 216 emits bright-field lightbeam 250 ₁ and gray-field light beam 252 ₁ towards aperture stop 218, atan outer diameter D_(TS) or, equivalently, D_(OS). Light beams 250 ₁ and252 ₁ pass through aperture stop 218. Referring back to FIGS. 3A, 3B and3C, light beams 250 ₁ and 252 ₁ then reach quarter wave plate 214. Atthis stage, light beams 250 ₁ and ²⁵² are circularly polarized in theopposite angular direction as light beam 244 ₁ (e.g., counterclockwise).Quarter wave plate 214 linearly polarizes light beams 250 ₁ and 252 ₁ ina direction perpendicular to the linear polarization of illuminatinglight beam 244 ₁. Light beams 250 ₁ and 252 ₁ then reach polarizing beamsplitter 210. Semi-transparent reflection plane 212 reflects light beams250 ₁ and 252 ₁ toward relay lens assembly 230.

[0106] Relay lens assembly 230, together with polarizing beam splitter210, produces an inverted image of telescope entrance pupil 218 at thepupil of annular mirror 232. Bright-field light beam 250 ₁ passesthrough the aperture of annular mirror 232 toward bright-field detector234. Bright-field detector 234 receives bright-field light beam 250 ₁and detects properties thereof. Annular mirror 232 reflects gray-fieldlight beam 252 ₁ toward gray-field detector 236. Gray-field detector 236receives gray-field light beam 252 ₁ and detects properties thereof.

[0107] With reference to FIG. 4B, Illuminating light beam 244 ₂ travelsa path similar to illuminating light beam 244 ₁, but on the oppositeside of optical axis 260. Objective lens 226 focuses illuminating lightbeam 244 ₂ onto a point 230 ₂ on wafer surface 202, located on theopposite side of optical axis 260 from 230 ₁, thereby producing abright-field light beam 250 ₂ and a gray-field light beam 252 ₂.Bright-field light beam 250 ₂ and gray-field light beam 252 ₂, completea similar path as bright-field light beam 250 ₁ and gray-field lightbeam 252 ₁, respectively, but on the opposite sides of optical axes 260,262 and 264.

[0108] Scanner 206 may also emit intermediate illuminating light beams(not shown) at intermediate moments in time (i.e., between the emissionof illuminating light beams 244 ₁ and 244 ₂). The intermediateilluminating light beams complete a similar path as illuminating lightbeams 244 ₁ and 244 ₂, but at intermediate angles relative to firstoptical axis 260. Thus, intermediate illuminating light beams reachintermediate points (not shown) on wafer surface 202 between points 230₁ and 230 ₂. Intermediate bright-field and gray-field light beams (notshown) are detected at bright-field detector 234 and gray-field detector236, respectively, at intermediate moments in time.

[0109] Thus, system 200 (FIG. 3) scans the line between points 230 ₁ and230 ₂ also known as the scan line, on wafer surface 202. The scan linelength L₁ is approximately equal to 2×F×θ₁.

[0110] The numerical aperture NA_(BF1) of bright-field light beam 250 ₁,also known as the bright-field numerical aperture, is equal toD_(BF1)2F, wherein D_(BF1) is the diameter of bright-field light beam250 ₁ and F is the focal length of objective lens 226. It is noted thatbright-field light beams 250 ₁ and 250 ₂, and intermediate bright-fieldlight beams in system 200, all have the same diameter D_(BF1), and henceall have the same numerical aperture NA_(BF1).

[0111] The numerical aperture NA_(GF1) of gray-field light beam 252 ₁,also known as the gray-field numerical aperture, is equal to D_(GF1/)2F,wherein D_(GF1) is the outer diameter of gray-field light beam 252 ₁ andF is the focal length of objective lens 226. It is noted that gray-fieldlight beams 252 ₁ and 252 ₂, and intermediate gray-field light beams insystem 200, all have the same outer diameter D_(GF1), and hence all havethe same numerical aperture NA_(GF1).

[0112] System 200 may further include other telescopes (not shown) inaddition to telescope 216. Some of these telescopes shall be describedherein below in conjunction with FIGS. 4D and 4E. Each telescope has adifferent magnification. The telescopes are mounted on a turret, a slide(both not shown), and the like, which enables interchanging telescopes.Thus, system 200 can operate at different modes of operation, whereineach mode of operation is characterized by a different magnification.

[0113] Reference is now made to FIGS. 4D and 4E. FIG. 4D is anillustration in detail of the aperture stop 218 and objective lensassembly 222 of system 200, a telescope 302, replacing telescope 216 andused in another mode of operation of system 200, and scanned wafersurface 202 (FIG. 3). FIG. 4E is an illustration in detail of theaperture stop 218 and objective lens assembly 222 of system 200, atelescope 322, replacing telescope 216 and used in a further mode ofoperation of system 200, and scanned wafer surface 202.

[0114] With reference to FIG. 4D, telescope 302 includes a firsttelescope lens 316 and a second telescope lens 318. The focal length offirst telescope lens 316 is 3 times greater than the focal length ofsecond telescope lens 318.

[0115] Telescope 302 receives an illuminating light beam 310 ₁ attelescope entrance pupil 304. It is noted that illuminating light beam310 ₁ has an identical illumination path (not shown) in system 200 (FIG.3), between scanner 206 and aperture stop 218, as illuminating lightbeam 244 ₁ (FIG. 3). The diameter of illuminating light beam 310 ₁ isalso equal to D_(IL). Telescope 302 produces an inverted image of thepupil of aperture stop 218, at the pupil of objective aperture stop 224,at a magnification ratio M=3. Telescope 302 emits illuminating lightbeam 310 ₁ at a diameter D_(BF2), and an angle θ₂. The linearmagnification and the angular magnification of telescope 302 are 3 and⅓, respectively. Accordingly, D_(BF2)=3×D_(IL), and θ₂=⅓×θ_(IL).

[0116] Objective lens assembly 222 focuses illuminating light beam 310 ₁onto a point 308 ₁, thereby producing a bright-field light beam 312 ₁and a gray-field light beam 314 ₁. Bright-field light beam 312 ₁ andgray-field light beam 314 ₁ have diameters D_(BF2) and D_(GF2=D) _(TS),respectively.

[0117] The diameter D_(BF2) of bright-field light beam 312 ₁ is equal to3×D_(IL). Accordingly, D_(BF2)=3×D_(BF1), and hence, the bright-fieldnumerical aperture NA_(BF2) for the mode of operation of system 200,illustrated in FIG. 4D, is equal to 3×NA_(BF1). The diameter D_(GF2) ofgray-field light beam 314 ₁ is equal to D_(OS)=D_(TS), and hence, thegray-field numerical aperture NA_(GF2) for this mode of operation isequal to NA_(GF1).

[0118] The scan line length L₂ for the mode of operation of system 200,illustrated in FIG. 4B is approximately equal to 2×F×θ₂ or,equivalently, L₂=⅓×L₁.

[0119] With reference to FIG. 4E, telescope 322 has a linearmagnification of M=⅓. Telescope 322 includes a first telescope lens 336and a second telescope lens 338. The focal length of first telescopelens 336 is 3 times less than the focal length of second telescope lens338. .

[0120] Telescope 322 receives an illuminating light beam 330 ₁ attelescope entrance pupil 324. Telescope 322 produces an inverted imageof pupil 324 at the pupil of objective aperture stop 224, at amagnification ratio M=⅓. Telescope 322 emits light beam 330 ₁ at adiameter D_(BF3), and an angle θ₃. The linear magnification and theangular magnification of telescope 302 are ⅓ and 3, respectively.Accordingly, D_(BF3)=⅓×D_(IL), and θ₃=3×θ_(IL).

[0121] Objective lens assembly 222 focuses illuminating light beam 330 ₁onto a point 328 ₁, thereby producing a bright-field light beam 332 ₁and a gray-field light beam 334 ₁. Bright-field light beam 332 ₁ has adiameter D_(BF3)=⅓×D_(BF1), and hence, the bright-field numericalaperture NA_(BF3) for this mode of operation is equal to ⅓×NA_(BF1).Gray-field light beam 334 ₁ has a diameter D_(GF3)=⅓×D_(TS)=⅓×D_(GF1),and hence, the gray-field numerical aperture NA_(BF3) for this mode ofoperation is equal to ⅓×NA_(GF1). It is noted that in the mode ofoperation of FIG. 4E, aperture stop 218 determines the diameter ofgray-field light beam 334 ₁.

[0122] The scanning resolution for system 200 is highly correlated withthe gray-field numerical aperture and to the bright-field numericalaperture. In addition, the scanning speed of system 200 is proportionalto the scan line length. Thus, by selecting different modes of operationusing different telescopes, the user of system 200 can choose between alow-resolution, high-speed scan, a high-resolution, low-speed scan andother modes in between.

[0123] System 200 uses a single (i.e., non interchangeable) objectivelens assembly together with a plurality of interchangeable telescopes,for the common illumination and collection path, as opposed toconventional systems which use a different objective lens assembly foreach magnification.

[0124] It is noted that a combination of a single high NA objective lensand a plurality of telescopes, provides a large collection area (i.e.,for collecting a collected light beam having a large diameter), at arelatively low cost, compared with that of a plurality of objective lensassemblies which are designed to exhibit that same large collectionarea. It is further noted that using an objective lens assembly having ahigh numerical aperture, provides a larger gray-field light beam, andhence, provides more information to the gray-field detector.

[0125] It is still further noted that the use of interchangeabletelescopes instead of interchangeable objective lens assemblies, reducesthe chance for contamination of the wafer, since the telescopes areisolated from the wafer, whereas the objective lens assembly is theelement of the optical system closest to the wafer and further notisolated there from.

[0126] According to another aspect of the disclosed technique, there isprovided novel optical structure for separating gray-field andbright-field light beams. According to this aspect, the combined lightbeam arrives first at an annular mirror, which separates there between.The annular mirror reflects the gray-field light beam to a gray-fielddetector and lets the bright-field light beam pass there through, towarda quarter wave plate and polarizing beam splitter.

[0127] Reference is now made to FIG. 5, which is a schematicillustration of a scanning system, generally referenced 360, constructedand operative in accordance with another embodiment of the disclosedtechnique.

[0128] In the example set forth in FIG. 5, system 360 is used forscanning a wafer surface 400. System 360 includes a laser light source362, a scanner 364, a polarizing beam splitter 366, a quarter wave plate368, an annular mirror 370, a relay lens assembly 372, an objective lensassembly 374, a bright-field detector 378 and a gray-field detector 380.Objective lens assembly 374 includes an objective aperture stop 376.Polarizing beam splitter 366 includes a semi-transparent reflectionplane 402.

[0129] Laser light source 362, scanner 364, polarizing beam splitter366, quarter wave plate 368, annular mirror 370, relay lens assembly372, objective lens assembly 374 and wafer surface 400 are positionedalong a first optical axis 392. First optical axis 392 is perpendicularto wafer surface 400. Scanner 364 is positioned between laser 362 andpolarizing beam splitter 366. Quarter wave plate 368 is positionedbetween polarizing beam splitter 366 and annular mirror 370. Relay lensassembly 372 is positioned between annular mirror 370 and objective lensassembly 374. Objective lens assembly 374 is positioned between relaylens assembly 372 and wafer surface 400.

[0130] Polarizing beam splitter 366 and bright-field detector 378 arepositioned along a second optical axis 394. In the present example,second optical axis 394 is perpendicular to first optical axis 392.

[0131] Annular mirror 370 and gray-field detector 380 are positionedalong a third optical axis 396. In the present example, third opticalaxis 396 is parallel to second optical axis 394.

[0132] Laser light source 362, scanner 364, polarizing beam splitter366, semi-transparent reflection plane 402, quarter wave plate 368,annular mirror 370, relay lens assembly 372, objective lens assembly374, objective entrance pupil 376, bright-field detector 378 andgray-field detector 380 are generally similar to laser light source 204,scanner 206, polarizing beam splitter 210, semi-transparent reflectionplane 212, quarter wave plate 214, annular mirror 232, relay lensassembly 230, objective lens assembly 222, objective aperture stop 224,bright-field detector 234 and gray-field detector 236 (FIG. 3),respectively.

[0133] Laser light source 362 emits a laser light beam 382 towardscanner 364. Scanner 364 receives laser light beam 382 and emits anilluminating light beam 384 toward polarizing beam splitter 366.Illuminating light beam 384 passes through semi-transparent plane 402and quarter wave plate 368, and from there, further through the apertureof annular mirror 370 toward relay lens assembly 372. Relay lensassembly 372 produces an inverted image of the pupil of annular mirror370, at the entrance pupil of objective lens assembly 374.

[0134] Objective lens assembly 374 focuses illuminating light beam 388onto a point 398 on wafer surface 400, thereby producing a bright-fieldlight beam 388 and a gray-field light beam 390. Objective lens assembly374 collects and collimates light beams 388 and 390, and directs lightbeams 388 and 390 toward relay lens assembly 372.

[0135] Relay lens assembly 376 produces an inverted image of theentrance pupil of objective lens assembly 374 at the pupil annularmirror 370. Annular mirror 370 reflects gray-field light beam 390 towardgray-field detector 380. Gray-field detector 380 receives gray-fieldlight beam 390 and detects properties thereof.

[0136] Bright-field light beam 388 passes through the aperture ofannular mirror 370 and from there, further through quarter wave plate368, towards polarizing beam splitter 366. Semi-transparent reflectionplane 402 reflects bright-field light beam 388 toward bright-fielddetector 378. Bright-field detector 378 receives bright-field light beam388 and detects properties thereof.

[0137] Polarizing beam splitter 366 and quarter wave plate 368 are usedin system 360 for reflecting bright-field light beam 388, and not forreflecting gray-field light beam 390. Thus, a smaller polarizing beamsplitter and a smaller quarter wave plate can be used in system 360,since the required sizes of polarizing beam splitter 366 and quarterwave plate 368 are determined by the bright-field diameter and scanningangle, and not by the gray-field diameter. It is noted that the use of asmaller polarizing beam splitter and a smaller quarter wave platesignificantly reduces the manufacturing cost of system 360, since thecost and size of the polarizing beam splitter are highly correlatedthere between.

[0138] According to another aspect of the disclosed technique,apodizators are positioned in the illumination path (and not in thecollection path), thereby controlling the shape of the illuminationlight beams, without directly affecting the shape of the respectivecollected bright-field and gray-field light beams. It is noted that theshape of the collected light beams may be indirectly affected by theapodizators, since the collected light beams depend on the respectiveilluminated light beams. According to this aspect, the illuminatinglight beam first passes through an apodizator located at a first pupil.The apodizator shapes the illuminating light beam at a predeterminedshape. The illuminating light beam then passes through a relay lensassembly, which produces an image of the first pupil at the entrancepupil of the objective lens.

[0139] Reference is now made to FIG. 6, which is a schematicillustration of a scanning system, generally referenced 420, constructedand operative in accordance with another embodiment of the disclosedtechnique.

[0140] In the example set forth in FIG. 6, system 420 is used forscanning a wafer surface 422. System 420 includes a laser light source424, a scanner 426, an apodizator 428, a polarizing beam splitter 430, aquarter wave plate 434, an objective lens assembly 436, relay lensassemblies 440 and 442, an annular mirror 444, a bright-field detector446 and a gray-field detector 448. Objective lens assembly 436 includesan objective entrance pupil 438 and an objective lens 466. Polarizingbeam splitter 430 includes a semi-transparent reflection plane 432.Laser light source 424, scanner 426, apodizator 428, relay lens assembly440, polarizing beam splitter 430, quarter wave plate 434, objectivelens assembly 436 and wafer surface 422 are positioned along a firstoptical axis 460. First optical axis 460 is perpendicular to wafersurface 422. Scanner 426 is positioned between laser light source 424and apodizator 428. Relay lens assembly 440 is positioned betweenapodizator 428 and polarizing beam splitter 430. Quarter wave plate 434is positioned between polarizing beam splitter 432 and objective lensassembly 436. Objective lens assembly 436 is positioned between quarterwave plate 434 and wafer surface 422.

[0141] Polarizing beam splitter 430, relay lens assembly 442, annularmirror 444 and bright-field detector 446 are positioned along a secondoptical axis 462. In the present example, second optical axis 462 isperpendicular to first optical axis 460. Relay lens assembly 442 ispositioned between polarizing beam splitter 430 and annular mirror 444.Annular mirror 444 is positioned between relay lens assembly 442 andbright-field detector 446.

[0142] Annular mirror 444 and gray-field detector 448 are positionedalong a third optical axis 464. In the present example, third opticalaxis 464 is parallel to first optical axis 460.

[0143] Laser light source 424, scanner 426, polarizing beam splitter430, semi-transparent reflection plane 432, quarter wave plate 434,annular mirror 444, objective lens assembly 436, objective entrancepupil 438, bright-field detector 446 and gray-field detector 448 aregenerally similar to laser light source 204, scanner 206, polarizingbeam splitter 210, semi-transparent reflection plane 212, quarter waveplate 214, annular mirror 232, objective lens assembly 222, objectiveaperture stop 224, bright-field detector 234 and gray-field detector 236(FIG. 3), respectively. Relay lens assemblies 440 and 442 are generallysimilar to relay lens 230 (FIG. 3).

[0144] In general, apodizator 428 has a minimal diameter of at leastD_(IL). In the present example, apodizator 428 is circular and has adiameter of D_(IL). A first portion of the area of apodizator 428 istransparent, while a second portion is opaque. For example, apodizator428 may include a transmitting outer annular region and an opaque innercircular region. Thus, apodizator 428 shapes light beams incident thereupon.

[0145] Annular mirror 444 is located at a pupil of the scanning system.In the present example, annular mirror 444 is oriented at 45 degreesrelative to axes 462 and 464. Semi-transparent reflection plane 432 isoriented at 45 degrees relative to optical axes 460 and 462.

[0146] Laser light source 424 emits a laser light beam 450 towardscanner 426. Scanner 426 receives laser light beam 450 and emits anilluminating light beam 452, at diameter D_(IL), toward apodizator 428.

[0147] Apodizator 428 shapes illuminating light beam 452 ₁ at apredetermined light beam shape.

[0148] Illuminating light beam 452 then reaches relay lens assembly 440.Relay lens assembly 440 produces an inverted image of the pupil ofapodizator 428, at the entrance pupil of objective lens assembly 436.Illuminating light beam 452 proceeds from relay lens assembly 440 topolarizing beam splitter 430. Illuminating light beam 452 passes throughpolarizing beam splitter and from there, further through quarter waveplate 434 toward objective lens assembly 436. Objective lens assembly436 focuses illuminating light beam 452 onto a point 458 on wafersurface 400, thereby producing a bright-field light beam 454 and agray-field light beam 456. Objective lens assembly 436 collects lightbeams 454 and 456, and directs them towards quarter wave plate 434.Light beams 454 and 456 pass through quarter wave plate 434 and arereflected from semi-transparent reflection plane 432, toward relay lensassembly 442. Relay lens assembly 442 produces an inverted image of theentrance pupil of objective lens assembly 436, at the pupil of annularmirror 444. Bright-field light beam 454 passes through the aperture ofannular mirror 444 and is detected at bright-field detector 446.Gray-field light beam 456 is reflected by annular mirror 464 and isdetected at gray-field detector 448.

[0149] System 420 may further include more apodizators (not shown) inaddition to apodizator 428. Each apodizator has different transmittingportions with different shapes or dimensions, and hence, each apodizatordetermines a different shape for the illuminating light beam. Theapodizators are mounted on a turret, a slide (both not shown), and thelike, which enables interchanging apodizators. Thus, system 420 canoperate at different modes of operation, wherein each mode of operationis characterized by different light beam shape, depending on theselected apodizator.

[0150] Reference is further made to FIGS. 7A, 7B and 7C. FIG. 7A is aschematic illustration of an apodizator 480, constructed and operativein accordance with a further embodiment of the disclosed technique. FIG.7B is a schematic illustration of objective lens assembly 436 of system420, scanned wafer surface 422 (FIG. 6), and an illuminating light beam490, which has already passed though apodizator 480 (FIG. 7A). FIG. 7Cis a schematic illustration of a bright-field light beam 500 and agray-field light beam 502, which are reflections and refractions ofilluminating light beam 490 (FIG. 7B), by wafer surface 422, travelingfrom wafer surface 422 and passing through objective lens assembly 436(FIG. 6).

[0151] With reference to FIG. 7A, apodizator 480 is a circular,transparent filter. Apodizator 480 has diameter D_(IL). Apodizator 480is uniform (i.e., fully transparent or filtering at specificwavelengths, and the like) and as such affects illuminating light beam490 in a uniform spatial manner.

[0152] With reference to FIG. 7B, objective lens assembly 436 includesan objective lens 466. Illuminating light beam 490 illuminates a point492 on wafer surface 422, after passing through apodizator 480 (FIG.7A).

[0153] With reference to FIG. 7C, wafer surface 422 scatters andreflects light from point 492, thereby producing a bright-field lightbeam 500 and a gray-field light beam 502. Light beams 500 and 502 areeventually detected at bright-field detector 446 and gray-field detector448 (FIG. 6), respectively.

[0154] Reference is further made to FIGS. 8A, 8B and 8C. FIG. 8A is aschematic illustration of another apodizator 520, constructed andoperative in accordance with another embodiment of the disclosedtechnique. FIG. 8B is a schematic illustration of objective lensassembly 436 of system 420, scanned wafer surface 422 (FIG. 6), and anilluminating light beam 530, which has already passed through apodizator520 (FIG. 8A). FIG. 8C is a schematic illustration of a bright-fieldlight beam 540 and a gray-field light beam 542, which are reflectionsand refractions of illuminating light beam 530 (FIG. 8B), by wafersurface 422, traveling from wafer surface 422 and passing throughobjective lens assembly 436 (FIG. 6).

[0155] With reference to FIG. 8A, apodizator 520 is a circular filterhaving diameter D_(IL). Apodizator 520 includes an outer region 522 andan inner region 524. Outer region 522 is opaque and annular, limited byouter diameter D_(IL) and an inner diameter D₁, wherein D₁<D_(IL). Innerregion 524 is transparent and circular, having diameter D₁.

[0156] With reference to FIG. 8B, illuminating light beam 530illuminates point 492 on wafer surface 422, after passing throughapodizator 520 (FIG. 8A). Illuminating light beam 530 has diameter D₁. Avolume 532 (shaded) around illuminating light beam 530, would have beena part of illuminating light beam 532, had it not been blocked by outerregion 522 of apodizator 520 (FIG. 8A). The cross-section of volume 532is annular, limited between inner diameter D₁ and outer diameter D_(IL).It is noted that the diameters of light beam 530 and volume 532, andsome of the other light beams in the description that follows, refer tothe diameter when the light beam is collimated.

[0157] With reference to FIG. 8C, wafer surface 422 scatters andreflects illuminating light beam 530 (FIG. 8B), thereby producing abright-field light beam 540 and a gray-field light beam 542. Light beams540 and 542 are eventually detected at bright-field detector 446 andgray-field detector 448 (FIG. 6), respectively.

[0158] Reference is further made to FIGS. 9A, 9B and 9C. FIG. 9A is aschematic illustration of another apodizator 560, constructed andoperative in accordance with a further embodiment of the disclosedtechnique. FIG. 9B is a schematic illustration of objective lensassembly 436 of system 420, scanned wafer surface 422 (FIG. 6), and anilluminating light beam 570, which has already passed through apodizator560 (FIG. 9A). FIG. 9C is a schematic illustration of a bright-fieldlight beam 580 and a gray-field light beam 582, which are reflectionsand refractions of illuminating light beam 570 (FIG. 9B), by wafersurface 422, traveling from wafer surface 422 and passing throughobjective lens assembly 436.

[0159] With reference to FIG. 9A, apodizator 560 is a circular filterhaving diameter D_(IL). Apodizator 560 includes an outer region 562 andan inner region 564. Outer region 562 is transparent and annular,limited between outer diameter D_(IL) and inner diameter D₁. Innerregion 564 is opaque and circular, having diameter D₁.

[0160] With reference to FIG. 9B, illuminating light beam 570illuminates point 492 on wafer surface 422. The cross-section ofilluminating light beam 570 is annular, limited between outer diameterD_(IL) and inner diameter D₁. Illuminating light beam 570 surrounds avolume 572 (shaded). Volume 572 has diameter D₁. Volume 572 would havebeen a part of illuminating light beam 570 had it not been blocked byinner region 564 of apodizator 560 (FIG. 9A). With reference to FIG. 9C,wafer surface 422 scatters and reflects illuminating light beam 570(FIG. 9B), thereby producing bright-field light beam 580 and agray-field light beam 582.

[0161] Reference is further made to FIGS. 10A, 10B and 10C. FIG. 10A isa schematic illustration of another apodizator 600, constructed andoperative in accordance with another embodiment of the disclosedtechnique. FIG. 10B is a schematic illustration of objective lensassembly 436 of system 420, scanned wafer surface 422 (FIG. 6), and anilluminating light beam 610, which has already passed through apodizator600 (FIG. 10A). FIG. 10C is a schematic illustration of a bright-fieldlight beam 620 and a gray-field light beam 622, which are reflectionsand refractions of illuminating light beam 610 (FIG. 10B), by wafersurface 422, traveling from wafer surface 422 and passing throughobjective lens assembly 436.

[0162] With reference to FIG. 10A, apodizator 600 is a circular filterhaving diameter D_(IL). Apodizator 600 includes an outer region 602, anintermediate region 604 and an inner region 606. Outer region 602 istransparent and annular, limited between outer diameter D_(IL) and innerdiameter D₁. Intermediate region 604 is opaque and annular, limitedbetween outer diameter D₁ and an inner diameter D₂, whereinD₂<D₁<D_(IL). Inner region 606 is transparent and circular, havingdiameter D₂.

[0163] With reference to FIG. 10B, illuminating light beam 610illuminates point 492 on wafer surface 422. Illuminating light beam 610has diameter D_(IL). Illuminating light beam 610 includes an outerportion 612 and an inner portion 616. The cross-section of outer portion612 is annular, limited between outer diameter D_(IL) and inner diameterD₁. The cross-section of inner portion 616 is circular, having diameterD₂. A volume 614 surrounds inner portion 616. Outer portion 616surrounds volume 614. The cross-section of volume 614 is annular,limited between outer diameter D₁ and inner diameter D₂. Volume 614would have been a part of illuminating light beam 610, had it not beenblocked by inner region 606 of apodizator 600 (FIG. 10A).

[0164] With reference to FIG. 10C, wafer surface 422 scatters andreflects illuminating light beam 610 (FIG. 10B), thereby producing abright-field light beam 620 and a gray-field light beam 622. Referenceis now made to FIGS. 11A, 11B and 11C. FIG. 11A is a schematicillustration of another apodizator, generally referenced 640,constructed and operative in accordance with a further embodiment of thedisclosed technique. FIG. 11B is a schematic illustration of objectivelens assembly 436 of system 420, scanned wafer surface 422 (FIG. 6), andan illuminating light beam 650, which has already passed throughapodizator 640 (FIG. 11A). FIG. 11C is a schematic illustration of abright-field light beam 660 and a gray-field light beam 662, which arereflections and refractions of illuminating light beam 650 (FIG. 11B),by wafer surface 422, traveling from wafer surface 422 and passingthrough objective lens assembly 436.

[0165] With reference to FIG. 11A, apodizator 640 is a circular filterhaving diameter D_(IL). Filter 640 includes a left region 642 and aright region 644. Left region 642 is opaque. Right region 644 istransparent.

[0166] With reference to FIG. 11B, illuminating light beam 650illuminates point 492 on wafer surface 422. A volume 652, would havebeen a part of illuminating light beam 650 had it not been blocked byright region 644 of apodizator 640 (FIG. 11A).

[0167] With reference to FIG. 11C, wafer surface 422 scatters andreflects illuminating light beam 650 (FIG. 11B), thereby producing abright-field light beam 660 and a gray-field light beam 662. It is notedthat light beams 500 and 502 (FIG. 7C), 540 and 542 (FIG. 8C), 580 and582 (FIG. 9C), 620 and 622 (FIG. 10C), and 660 and 662 (FIG. 11C), allhave the same diameters. However, these light beams generally differ inother properties, since their respective illuminating light beams aregenerally different.

[0168] Reference is now made to FIG. 12, which is a schematicillustration of a dynamic apodizator 680 and a controller 690,constructed and operative in accordance with a further embodiment of thedisclosed technique.

[0169] Dynamic apodizator 680 is coupled to controller 690. It is notedthat controller 690 may be further coupled with other elements of thescanning system, a user interface, a combination thereof, and the like.Dynamic apodizator 680 includes a plurality of light valve elements,generally referenced 682 _(i), such as light valve elements 682 ₁, 682₂, and 682 _(N), arranged in a two-dimensional array.

[0170] Light valve elements are components, which have an ability toinfluence light in at least one way. Some of these ways are, forexample: scattering, converging, diverging, absorbing, imposing apolarization pattern, influencing a polarization pattern which, forexample, may be by rotation of a polarization plane, influencing wavelength, diverting a beam's direction for example by using digitalmicro-mirror display (also known as DMD) or by using field effect,influencing phase, interference techniques, which either blocks ortransfers a portion of beam of light and the like. Activation of lightvalve elements, which are utilized by the disclosed technique, can beperformed either electrically, magnetically or optically. Commonly usedlight valve elements are liquid crystal based elements, which eitherrotate or create and enforce a predetermined polarization axis. In theexample set forth in FIG. 12, light valve elements 680 _(i) have twostates, transmitting and non-transmitting. A light valve in thetransmitting state, transmits light there through, and hence, lightincident there upon reaches bright-field detector 446 (FIG. 6). A lightvalve in the non-transmitting state prevents light from reachingbright-field detector 446.

[0171] Depending on a signal from controller 690 to dynamic apodizator680, each of light valves 680 _(i) is either transparent or opaque. Inthe present example, light valve elements 682 ₁ and 682 _(N) aretransparent, and cell 682 ₂ is opaque.

[0172] According to another aspect of the disclosed technique, system420 (FIG. 6) is complemented by bright-field filters, which block aselected portion of the bright-field light beam before the bright-fieldlight beam reaches the bright-field detector.

[0173] Reference is now made to FIGS. 13A, 13B and 13C. FIG. 13A is aschematic illustration of a bright-field filter 700. FIG. 13B is aschematic illustration of bright-field filter 700 (FIG. 13A) and abright-field light beam 720 incident there upon and partiallytransmitted there through. FIG. 13C is a schematic illustration ofobjective lens assembly 436 of system 420 and scanned wafer surface 422(FIG. 6), illuminating light beam 570 and volume 572 (FIG. 9A), andbright-field light beam 720 (FIG. 13B) and a gray-field light beam 742,which are reflections and refractions of illuminating light beam 720, bywafer surface 422.

[0174] With reference to FIG. 13A, bright-field filter 700 is a circularfilter having diameter D_(IL) Bright-field filter 700 includes an outerregion 702 and an inner region 704. Outer region 702 is opaque andannular, limited between outer diameter D_(IL) and inner diameter D₁.Inner region 704 is transparent and circular, having diameter D₁.

[0175] With reference to FIG. 13B, bright-field light beam 720 reachesbright-field filter 700 at diameter D_(IL). Bright field light beam ispartially transmitted through bright-field filter 700 at diameter D₁. Avolume 722 (shaded) around bright-field light beam 720, would have beena part of bright-field light beam 720 had it not been blocked by outerregion 702 of bright-field filter 700 (FIG. 13A). The cross-section ofvolume 722 is annular, limited between inner diameter D₁ and outerdiameter D_(IL).

[0176] With reference to FIG. 13C, objective lens assembly 436 focusesilluminating light beam 570 onto a point 492 on wafer surface 422. Wafersurface 422 scatters and reflects illuminating light beam 570, therebyproducing bright-field light beam 720 (FIG. 13B) and gray-field lightbeam 742. Volume 572 is a part of bright-field light beam 720. Asmentioned above, volume 572 would have been a part of illuminating lightbeam 570 had it not been blocked by inner region 564 of apodizator 560(FIG. 9A). The portion of bright-field light beam having the samegeometrical location as illuminating light beam 570, is eventuallyblocked by bright-field filter 700 (FIG. 13B).

[0177] Thus, with reference to the system of FIG. 13C, the light whichwould eventually reach the bright-field detector, does not coincide withthe illuminating light beam. This situation is similar to dark-fieldmicroscopes. In a dark-field microscope, the inspected surface isilluminated from significantly flat angles (i.e., almost parallel to theinspected surface), and the reflected light is detected at nearly rightangles, above the inspected surface. The preceding situation is similarin that the angles at which the illuminating light hits the inspectedsurface and the angles at which detected light are reflected from theinspected surface, do not overlap.

[0178] In a further embodiment of the disclosed technique, continuousrange magnification replaces the discrete values magnification which wasprovided by the interchangeable telescopes. A system according to thisembodiment utilizes optical elements with zoom capabilities, to replacethe multiple telescopes. Zoom capable optical element may include ateleconverter lens, a zoom capable telescope and the like. Such zoomcapable optical elements allow adjustment of magnification level in agiven range, without replacing the telescope. The present embodiment mayinclude a single zoom capable optical element or a plurality ofinterchangeable zoom capable optical elements.

[0179] Reference is now made to FIG. 14, which is a schematicillustration of a system, generally referenced 750, for scanning a wafersurface, according to another embodiment of the disclosed technique.System 750 includes an automatic feedback magnification architecture forsuspected defect analysis. In the present example, system 750 is usedfor scanning a wafer surface 752.

[0180] System 750 includes an objective lens assembly 754, a telescope756, a controller 760, a teleconverter lens assembly 758 with zoomcapabilities, an analysis module 762, a sensor 764 and an optical path(not detailed) 766.

[0181] Two elements are considered optically associated there betweenwhen they are positioned so as to allow light from one of the elementsto enter the other element (e.g., by being placed along the same opticalaxis).

[0182] Telescope 756 is optically associated with objective lensassembly 754 and with teleconverter lens assembly 758. Teleconverterlens assembly 758 is further optically associated via optical path 766(not detailed) to sensor 764. Analysis module 762 is coupled to sensor764 and to controller 760. Controller 760 is further coupled toteleconverter lens assembly 758. System 750 may further include anilluminating light source (not shown).

[0183] System 750 is designed to allow a suspected defect detected onwafer 752 to be examined in increasingly greater levels ofmagnification, by using a continuous magnification level range. Acontinuous magnification range is achieved by optically associatingteleconverter lens assembly 758 having zoom capabilities, with telescope756. Teleconverter lens assembly 758 and telescope 756 both define acombined magnification range. Changing the optical setting ofteleconverter lens assembly 758 effectively changes the focal length oftelescope 756, thereby changing the combined magnification level, withinthe combined magnification range. Teleconverter lens assembly 758further changes the angular width of illuminating light beamstransmitted through teleconverter lens assembly 758 and telescope 756,thereby allowing control over scanning resolution of the inspected wafersurface.

[0184] Light from illuminating light source (not shown in Figure) isincident on wafer 752, either by oblique illumination, or by directillumination via teleconverter lens assembly 758, telescope 756, andobjective lens assembly 754. The angular width of the obliqueilluminating light is set by optical elements in the obliqueilluminating beam path (not shown in Figure). The angular width ofdirect illuminating beam can be modified by employing the zoomcapabilities of teleconverter lens assembly 758.

[0185] Objective lens assembly 754 collects light reflected andscattered from wafer surface 752. Objective lens assembly 754 directslight to sensor 764 via telescope 756 and teleconverter lens assembly758 and further via optical path 766 (not detailed in Figure). Sensor764 detects light received from teleconverter lens assembly 758 andprovides data respective of the detected light to analysis module 762.Analysis module 762 analyzes the received data and determines whether asuspected defect is classified as an actual defect, is classified as adetection error (no defect), or requires further analysis.

[0186] If the suspected defect is classified as an actual defect,analysis module 762 reports the detected defect and resumes scanning forfurther defects. If the suspected defect is determined to be a detectionerror, normal scanning is resumed. If the suspected defect is determinedto require further analysis, then analysis module 762 determines therequired magnification level, and provides a command to controller 760,to operate teleconverter lens assembly 758. Controller 760 operatesteleconverter lens assembly 758 so as to adjust the magnification to thelevel determined by analysis module 762. System 750 then scans suspecteddefect area and repeats the process outlined using increasingly highermagnification levels, until suspected defect is classified.

[0187] Reference is now made to FIG. 15, which is a schematicillustration of a system, generally referenced 780, for scanning a wafersurface, according to a further embodiment of the disclosed technique.System 780 includes an automatic feedback magnification architecture forsuspected defect analysis. In the present example, system 780 is usedfor scanning a wafer surface 782.

[0188] System 780 includes an objective lens assembly 784, a telescope786, a teleconverter lens assembly 788 with zoom capabilities, acontroller 790, an analysis module 792, a sensor 794 and an optical path(not detailed) 796.

[0189] Teleconverter lens assembly 788 is optically associated withobjective lens assembly 784 and with telescope 786. Telescope 786 isfurther optically associated via optical path 796 (not detailed) tosensor 794. Analysis module 792 is coupled to sensor 794 and tocontroller 790, controller 790 is further coupled to teleconverter lensassembly 788. System 780 may further include an illuminating lightsource (not shown).

[0190] System 780 differs from system 750 (FIG. 14) in that theteleconverter lens is located between the telescope and the objectivelens assembly (i.e., and not after the telescope and objective lensassembly).

[0191] Reference is now made to FIG. 16, which is a schematicillustration of a front end optical assembly, generally referenced 800,for scanning a wafer surface, according to another embodiment of thedisclosed technique. Front end optical assembly 800 may be incorporatedin a scanning system with image analysis and automatic feedback forsuspected defect analysis. In the present example, front end opticalassembly 800 is used for scanning a wafer surface 802.

[0192] Front end optical assembly 800 includes an objective lensassembly 804 and a telescope 806 with zoom capabilities (also calledzoom telescope). Telescope 806 may be further coupled to a controller(not shown), which controls the magnification thereof. Objective lensassembly 804 is optically associated with telescope 806. Telescope 806is further optically associated via an optical path to a sensor (notshown). Front end optical assembly 800 is designed to allow a suspecteddefect detected on wafer 802 to be examined at increasingly greaterlevels of magnification, by using a continuous magnification range.

[0193] A continuous magnification range is achieved by utilizing atelescope 806, having zoom capabilities within a magnification range.Changing the zoom level setting for telescope 806, changes themagnification level, within the magnification range. Telescope 806further changes the numerical aperture of the illuminating light beam,thereby allowing control over the scanning resolution of the inspectedsurface.

[0194] Light from an illuminating light source (not shown) is incidenton wafer 802, either by oblique illumination, or by direct illuminationvia telescope 806 and objective lens assembly 804. The numericalaperture of oblique illuminating light is set by optical elements inoblique illuminating beam path (not shown). The numerical aperture ofdirect illuminating light beams can be modified by employing the zoomcapabilities of telescope 806.

[0195] Front end optical assembly 800 differs from systems 750 and 800,in that the zoom capable optical element is the telescope 806 (i.e., nota teleconverter lens). Other aspects of front end assembly 800 (e.g.,automatic magnification change) are similar to those detailed for system750.

[0196] Systems 750 and 780 (FIGS. 14 and 15), and front end assembly 800(FIG. 16) reduce the need for replacing the telescope when magnificationand scanning resolution changes are required, and further eliminate (orsignificantly reduce) the need for operator intervention.

[0197] Reference is now made to FIG. 17, which is a schematicillustration of a method for operating either of systems 750, 780 andfront end assembly 800 of FIGS. 14, 15 and 16, respectively, operativein accordance with another embodiment of the disclosed technique.

[0198] In procedure 850, the wafer surface is scanned for suspecteddefects, by detecting an image of a portion of the wafer surface. In theexample set forth in FIG. 14, the wafer surface 752 is scanned byilluminating light beams, and collected light is transmitted to sensor764 via the optical path.

[0199] In procedure 852, the presence of defects is detected, byanalyzing the detected image. In the example set forth in FIG. 14,analysis module 762 analyzes data provided from sensor 764, to determineareas of suspected defects.

[0200] If the presence of defects is not detected, then the systemresumes normal processing (procedure 858). Otherwise, if the presence ofa defect is detected, then this defect is marked and reported (procedure860). Finally, if the detection of the presence of defects isinconclusive, then the system proceeds to procedure 854.

[0201] In procedure 854, a zoom level which is required for furtheranalysis, is calculated. In the example set forth in FIG. 14, analysismodule 762, calculates a zoom level which is required for furtheranalysis.

[0202] In procedure 856, the zoom level is adjusted to the levelcalculated in procedure 854. In the example set forth in FIG. 14,analysis module 762 provides a command to controller 760 to operateteleconverter lens assembly 758. Controller 760 then operatesteleconverter lens assembly 758 to change the magnification level tothat calculated by analysis module 762. After the zoom level is adjustedin procedure 856, the system proceeds to procedure 850 to performfurther analysis of suspected defect areas. In the example set forth inFIG. 14, the suspected area is scanned again using a highermagnification level. The process illustrated is repeated until thesuspected defect is classified as an actual defect or a false detection.

[0203] According to another aspect of the disclosed technique, there isprovided a novel structure of the gray-field detector. The novelgray-field detector is divided into a plurality of zones. Each zone isdetected independently, and thus, the combined results providesupplementary information about the inspected wafer surface.

[0204] Reference is now made to FIG. 18, which is a schematicillustration of a multi-zone gray-field detector, generally referenced900, constructed and operative in accordance with a further embodimentof the disclosed technique. Multi-zone gray-field detector 900 includesa gray-field collector 902, light guides 910 ₁, 910 ₂, 910 ₃, 910 ₄, 904₅ and 904 ₆, and light detectors 904 ₁, 904 ₂, 904 ₃, 904 ₄, 904 ₅ and904 ₆.

[0205] Gray-field pupil collector 902 is circular at a diameter D_(GF).Gray-field collector 902 is located at a pupil of the scanning system.It is noted that diameter D_(GF) may be set at any size, depending onthe size of the image, which is produced at the pupil of gray-fieldcollector 902. Gray-field collector 902 includes a right section 906_(R), a left section 906 _(L), a top section 906 _(T), a bottom section906 _(B), a top-right section 906 _(TR), a bottom-right section 906_(BR), a top-left section 906 _(TL), a bottom-left section 906 _(BL) anda central section 906 _(C). Central section 906 _(C) is positioned atthe center of light collector D_(GF). Central section 906 _(C) is asquare of side S.

[0206] Right section 906 _(R) is a horizontal strip of width S. The leftboundary of right section 906 _(R) is a straight line coinciding withthe right boundary of central section 906 _(C). The top boundary ofright section 906 _(R) is a straight line extending the top boundary ofcentral section 906 _(C). The bottom boundary of right section 906 _(R)is a straight line extending the bottom boundary of central section 906_(C). The right boundary of right section 906 _(R) is an arc coincidingwith a portion of the boundary of gray-field collector 902. Left section906 _(L) and right section 906 _(R) are symmetrical with respect to thevertical diameter of gray-field collector 902. Top section 906 _(T) andbottom section 906 _(B) are identical to right section 906 _(R) and leftsection 906 _(L), but rotated by 90 degrees there from. Top-rightsection 906 _(TR) has a left boundary coinciding with the right boundaryof top section 906 _(T), a bottom boundary coinciding with the topboundary of right section 906 _(R), and a top-right boundary coincidingwith a portion of the boundary of gray-field collector 902. Similarly,bottom-right section 906 _(BR), top-left section 906 _(TL) andbottom-left section 906 _(BL) complete the circular region occupied bygray-field collector 902.

[0207] Each section of gray-field collector 902, except for centralsection 906 _(C), is optically coupled to a respective light detector ina manner that the light incident upon that section, is directed to thatrespective light detector. It is noted that more than one section can beoptically coupled to the same light detector. Different light guidingelements can be used for optically coupling the sections to theirrespective light detectors, such as optic fiber, specific shape moldedtransparent light guides, mirrors, and the like. In the example setforth in FIG. 18, each of light guides 910 ₁, 910 ₂, 910 ₃, 910 ₄, 910 ₅and 910 ₆, includes a plurality of optical fibers.

[0208] Light guide 910 ₁ optically couples top-left section 906 _(TL) tolight detector 904 ₁. Light guide 910 ₂ optically couples top-rightsection 906 _(TR) to light detector 904 ₂. Light guide 910 ₃ opticallycouples left section 906 _(L) and right section 906 _(R) to lightdetector 904 ₃. Light guide 910 ₄ optically couples bottom-left section906 _(BL) to light detector 904 ₄. Light guide 910 ₅ optically couplesleft section 906 _(L) and right section 906 _(R) to light detector 904₅. Light guide 910 ₆ optically couples bottom section 906 _(L) and topsection 906 _(T) to light detector 904 ₆.

[0209] It is noted that gray-field detector 900 may include additionaloptical elements, such as a relay lens assembly, which is located infront of the gray-field pupil. Such a relay lens assembly, produces thegray-field portion of the image of a pupil of the scanning system, atgray-field collector 902.

[0210] It is further noted that, unlike conventional gray-fielddetectors which provide information respective of the amount ofgray-field light, light detectors 904 ₁, 904 ₂,904 ₃, 904 ₄, 905 ₅ and904 ₆ provide information respective of angular and spatial distributionof the gray-field light. The information provided by light detectors 904₁, 904 ₂, 904 ₃, 904 ₄, 905 ₅ and 904 ₆, significantly increases theamount and quality of inspection information, and hence ability todetect defects in the scanned surface.

[0211] Several aspects of the disclosed technique, which are illustratedin the drawings discussed hereinabove, may be combined in a singlesystem. Reference is now made to FIG. 19, which is a schematicillustration of a system, generally referenced 1000, for scanning awafer surface, constructed and operative in accordance with anotherembodiment of the disclosed technique. In the example set forth in FIG.19, system 1000 is used for scanning a surface 1002. It is noted thatsystem 1000 is not drawn to scale. System 1000 includes a laser lightsource 1004, a scanner 1006, an apodizator 1008, a relay lens assembly1010, a polarizing beam splitter 1012, a quarter wave plate 1014, anannular mirror 1016, an aperture stop 1036, a telescope 1018, anobjective lens assembly 1020, a bright-field filter 1026, a bright-fielddetector 1022 and a gray-field detector 1024.

[0212] Laser light source 1004, scanner 1006, aperture stop 1036,telescope 1018 and objective lens 1020 are generally similar to laserlight source 204, scanner 206, aperture stop 218, telescope 216 andobjective lens assembly 222 (FIG. 3), respectively. Objective lensassembly 1020 has a high numerical aperture. System 1000 includesadditional telescopes (not shown) which are interchangeable withtelescope 1020.

[0213] Polarizing beam splitter 1012, quarter wave plate 1014, annularmirror 1016 and bright-field detector 1022 are generally similar topolarizing beam splitter 366, quarter wave plate 368, annular mirror 370and bright-field detector 378 (FIG. 5), respectively. Gray-fielddetector 1024 is generally similar to multi-zone gray-field detector 900(FIG. 18).

[0214] Apodizator 1008 and relay lens assembly 1010 are generallysimilar to apodizator 428 and relay lens assembly 440 (FIG. 6),respectively. Bright-field filter 1026 is generally similar tobright-field filter 700 (FIG. 13B). System 1000 may further includeadditional apodizators (not shown) which are interchangeable withapodizator 1008.

[0215] Laser light source 1004, scanner 1006, apodizator 1008, relaylens assembly 1010, polarizing beam splitter 1012, quarter wave plate1014, annular mirror 1016, telescope 1018, objective lens assembly 1020and wafer surface 1012 are positioned along a first optical axis 1030.First optical axis 1030 is perpendicular to surface 1002.

[0216] Scanner 1006 is positioned between laser light source 1004 andapodizator 1008. Relay lens assembly 1010 is positioned betweenapodizator 1008 and polarizing beam splitter 1012. Quarter wave plate1014 is positioned between polarizing beam splitter 1012 and annularmirror 1016. Aperture stop 1036 is positioned between annular mirror1016 and telescope 1018. Objective lens assembly 1020 is positionedbetween telescope 1018 and surface 1002.

[0217] Polarizing beam splitter 1012, bright-field filter 1026 andbright-field detector 1022 are positioned along a second optical axis1032. Bright-field filter 1026 is positioned between polarizing beamsplitter 1012 and bright-field detector 1022. In the present example,second optical axis 1032 is perpendicular to first optical axis 1030.

[0218] Annular mirror 1016 and gray-field detector 1024 are positionedalong a third optical axis 1034. In the present example, third opticalaxis 1034 is parallel to second optical axis 1032. It is noted that thearrows on optical axes 1030, 1032 and 1034, merely indicate the generaldirections of light beam progression there along and not the light beamsthemselves, which are not shown. Polarizing beam splitter 1012 includesa semi-transparent reflection plane 1026. In the present example,semi-transparent reflection plane 1026 is oriented at 45 degreesrelative to optical axes 1030 and 1032. Annular mirror 1016 is alsooriented at 45 degrees relative to optical axes 1030 and 1032.

[0219] Laser 1004 emits a laser light beam (not shown) toward scanner1006. Scanner 1006 receives the laser light beam and produces anilluminating light beam (not shown). The illuminating beam passessuccessively through scanner 1006, apodizator 1008, relay lens assembly1010, polarizing beam splitter 1012, quarter wave plate 1014, annularmirror 1016, aperture stop 1036, telescope 1018, and finally objectivelens assembly 1020. The illuminating light beam then reaches surface1002. Surface 1002 reflects the illuminating light beam, therebyproducing a bright-field light beam and a gray-field light beam (bothnot shown). The combined bright-field and gray-field light beam passesthrough objective lens assembly 1020, aperture stop 1036 and telescope1018. Annular mirror 1016 reflects the gray-field light beam towardgray-field detector 1024, which detects the intensity thereof. Thebright-field light beam passes through the aperture of annular mirror1016, and further through quarter wave plate 1014. Semi-transparentreflection plane 1026 reflects the bright-field light beam towardsbright-field detector 1022, which detects the intensity thereof.

[0220] It is noted that the combination of the single, high numericalaperture objective lens assembly 1020, the annular mirror 1016 and thepolarizing beam splitter 1012, significantly increases the gray-fieldnumerical aperture at an efficient cost, thereby significantlyincreasing the amount of data which is accumulated in the scanningprocess. This is due to the fact that the novel optical structure of theannular mirror 1016 and polarizing beam splitter 1012, does not limitthe numerical aperture of the gray-field light beam which is transferredthereby toward the gray-field detector. As a result, the maximalnumerical aperture of this gray-field image mostly depends on thenumerical aperture of the objective lens assembly 1020.

[0221] It is further noted that the combination of apodizator 1008 andbright-field filters 1026, enables a mode of operation similar to thatof a dark-field microscope, in that the illuminating light is incidenton the wafer surface at angles which are not detected by thebright-field detector. Combined with telescope 1018, the combination ofapodizator 1008 and bright-field filters 1026, further enhances thesimilarity to microscope dark-field mode. It is noted that sometelescopes are designed so as to increase the numerical aperture of theilluminating light beam and the bright-field light beam. Thus, theilluminating light and the detected light still do not intersect, butthe surface is illuminated from angles which are further flattened,closer to the angles of illumination in dark-field microscopes.

[0222] It is still further noted that system 1000 is characterized by ahigh gray-field numerical aperture, which significantly increases theinformation which is embedded in the gray-field light beam. Thisinformation is detected at great detail by gray-field detector 1024.

[0223] Reference is now made to FIG. 20, which is a schematicillustration of a method for inspecting a surface, in accordance withanother embodiment of the disclosed technique. In procedure 1100, anilluminating light beam is directed through an apodizator and a relaylens assembly. In the example set forth in FIG. 19, laser 1004 andscanner 1006 produce the illuminating light beam (not shown), which isdirected through apodizator 1008 and relay lens assembly 1010.

[0224] In procedure 1102, the illuminating light beam is directedthrough a polarizing beam splitter, a quarter wave plate and an annularmirror. In the example set forth in FIG. 1004, the illuminating lightbeam is directed through polarizing beam splitter 1012 and quarter waveplate 1014.

[0225] In procedure 1104, the illuminating light beam is directedthrough a selected telescope and an objective lens assembly, therebyfocusing the illuminating light beam onto a point on the inspectedsurface. In the example set forth in FIG. 19, the illuminating lightbeam is directed through telescope 1018 and objective lens assembly1020, whereby the illuminating light beam is focused onto a point oninspected surface 1002.

[0226] In procedure 1106, a portion of the reflected or scattered lightis collected at the objective lens assembly, and the collected light isdirected back through the telescope. In the example set forth in FIG.19, the illuminating light beam reflected and scattered from surface1002, and a portion of the scattered and reflected light is directedback through objective lens assembly 1020 and telescope 1018.

[0227] In procedure 1108, gray-field light beam is reflected by anannular mirror, towards a light detector. In the example set forth inFIG. 19, annular mirror 1016 reflects the gray-field light beam towardsgray-field detector 1024.

[0228] In procedure 1110, a bright-field light beam is directed throughthe aperture of the annular mirror and the quarter wave plate. In theexample set forth in FIG. 19, the bright-field light beam passes throughthe aperture of annular mirror 1016, and further through quarter waveplate 1014.

[0229] In procedure 1112, the bright-field light beam is reflected, atthe polarizing beam, towards a light detector. In the example set forthin FIG. 19, semi-transparent reflection plane 1026 reflects thebright-field light beam towards bright-field detector 1022. It is notedthat procedures 1108 and 1110 are performed independently and may begenerally executed in any order or concurrently.

[0230] It will be appreciated by persons skilled in the art that thedisclosed technique is not limited to what has been particularly shownand described hereinabove. Rather the scope of the disclosed techniqueis defined only by the claims, which follow.

1. System for scanning a surface, comprising: a light source producingan illuminating light beam; an objective lens assembly, located betweensaid light source and said surface; a plurality of interchangeabletelescopes, a selected one of said interchangeable telescopes beinglocated between said light source and said objective lens assembly; andat least one light detector, wherein at least one of said at least onelight detector detects at least a portion of a reflected light beamreceived from said selected telescope.
 2. The system of claim 1 furthercomprising a polarizing beam splitter located between said selectedtelescope and said light source, admitting said illuminating light beamand deflecting said at least a portion of a reflected light beamreceived from said selected telescope toward said at least one of saidat least one light detector.
 3. The system of claim 1 wherein saidilluminating light beam travels through said polarizing beam splitter,said selected telescope and said objective lens assembly toward saidsurface, which in turn reflects said reflected light beam, wherein atleast a portion of said reflected light beam travels through saidobjective lens assembly and said selected telescope, wherein saidpolarizing beam splitter deflects at least a portion of said at leastportion of said reflected light beam, toward said light detector.
 4. Thesystem of claim 2 further comprising an annular mirror located betweensaid polarizing beam splitter and said at least one of said at least onelight detector, wherein said annular mirror admits the bright-fieldportion of said at least a portion of said reflected light beam throughan aperture therein, and wherein said annular mirror reflects thegray-field portion of said at least a portion of said reflected lightbeam toward selected others of said at least one light detector.
 5. Thesystem of claim 4 further comprising a relay lens assembly, locatedbetween said polarizing beam splitter and said annular mirror, producingan image of said surface, on said aperture.
 6. The system of claim 2further comprising an annular mirror located between said polarizingbeam splitter and said at least one of said at least one light detector,wherein said annular mirror admits a central portion of said at least aportion of said reflected light beam through an aperture therein, andwherein said annular mirror reflects a non-central portion of said atleast a portion of said reflected light beam toward selected others ofsaid at least one light detector.
 7. The system of claim 6 furthercomprising a relay lens assembly, located between said polarizing beamsplitter and said annular mirror, producing an image of said surface, onsaid aperture.
 8. The system of claim 1, wherein said light sourceproduces said illuminating light beam, so as to scan said surface. 9.The system of claim 1, wherein said surface is selected from the listconsisting of: a wafer; a mask; printed material; and fabric.
 10. Thesystem of claim 1, wherein said objective lens assembly is located at afixed distance from said surface.
 11. The system of claim 1, whereinsaid objective lens assembly is located at a fixed distance from saidsurface, for each selection of said interchangeable telescopes.
 12. Thesystem of claim 1, further comprising a quarter wave plate locatedbetween said polarizing beam splitter and said selected interchangeabletelescope, wherein said illuminating light beam is linearly polarizedbefore passing through said quarter wave plate.
 13. The system of claim1, further comprising an interchanging mechanism, wherein at leastselected ones of said interchangeable telescopes are located on saidinterchanging mechanism, interchanging to a selected telescope when oneis selected.
 14. The system of claim 13, wherein said interchangingmechanism is selected from the list consisting of: a turret; and aslide.
 15. The system of claim 1, further comprising an analysis module,coupled to said at least one light detector.
 16. The system of claim 1,further including a teleconverter lens assembly, optically associatedwith said selected interchangeable telescope.
 17. The system of claim16, wherein said teleconverter lens assembly is located between saidselected interchangeable telescope and said objective lens assembly. 18.The system of claim 16, wherein said selected interchangeable telescopeis located between said teleconverter lens assembly and said objectivelens assembly.
 19. The system of claim 16, further comprising acontroller coupled to said teleconverter lens assembly, wherein saidcontroller operates said teleconverter lens assembly to adjust thecombined magnification of said teleconverter lens assembly and saidselected interchangeable telescope.
 20. The system of claim 19, furthercomprising an analysis module, coupled to said at least one lightdetector and to said controller, wherein said analysis module analyzeslight readings provided from said at least one light detector, for thepurpose of detecting defects, said analysis module determining a newmagnification level when detecting a suspected defect, and instructingsaid controller to operate said teleconverter lens assembly to adjust tosaid combined magnification to said new magnification level.
 21. Thesystem of claim 1, wherein at least one of said interchangeabletelescopes comprises a zoom telescope.
 22. The system of claim 21,further comprising a controller coupled to said zoom telescope, whereinsaid controller operates said zoom telescope to adjust the magnificationof said zoom telescope.
 23. The system of claim 22, further comprisingan analysis module, coupled to said at least one light detector and tosaid controller, wherein said analysis module analyzes light readingsprovided from said at least one light detector, for the purpose ofdetecting defects, said analysis module determining a new magnificationlevel when detecting a suspected defect, and instructing said controllerto operate said zoom telescope to adjust to said magnification to saidnew magnification level.
 24. The system of claim 1, further comprisingan annular mirror located between said light source and said selectedinterchangeable telescope, said annular mirror admitting saidilluminating light beam and deflecting at least a portion of a reflectedlight beam received from said selected interchangeable telescope towardat least one of said at least one light detector.
 25. The systemaccording to claim 24, further comprising a polarizing beam splitter,located between said light source and said annular mirror, admittingsaid illuminating light beam and deflecting at least a portion of saidreflected light beam admitted through said annular mirror toward atleast another of said at least one light detector.
 26. The systemaccording to claim 24, wherein said at least one of said at least onelight detector is a gray-field light detector.
 27. The system accordingto claim 24, wherein said at least other of said at least one lightdetector is a bright-field light detector.
 28. The system of claim 24,further comprising a quarter wave plate located between said polarizingbeam splitter and said annular mirror, wherein said illuminating lightbeam is linearly polarized before passing through said quarter waveplate.
 29. The system of claim 24, wherein said at least portion of saidreflected light beam, reflected by said annular mirror, is defined as agray-field reflected light beam.
 30. The system of claim 24, whereinlight reflected by said annular mirror, is defined as a gray-fieldreflected light beam.
 31. The system of claim 25, wherein lightreflected by said polarizing beam-splitter, is defined as a bright-fieldreflected light beam.
 32. The system of claim 24, wherein the innerdiameter of said annular mirror is in the order of the diameter of saidilluminating light beam, right before passing through said annularmirror.
 33. The system of claim 25, wherein the deflecting plane of saidpolarizing beam splitter is limited to the order of the width of said atleast a portion of said reflected light beam admitted through saidannular mirror, right before being deflected by said polarizing beamsplitter.
 34. The system of claim 24, further comprising a relay lensassembly located between said annular mirror and said selectedinterchangeable telescope.
 35. The system of claim 24, wherein saidlight source produces said illuminating light beam, so as to scan saidsurface.
 36. The system of claim 1, further comprising: an apodizatorlocated between said light source and said selected interchangeabletelescope; and a relay lens assembly located between said apodizator andsaid selected interchangeable telescope.
 37. The system according toclaim 36, wherein said light source produces an image of saidilluminating light beam on said apodizator, wherein said apodizatorblocks at least a portion of said illuminating light beam, and whereinsaid relay lens assembly images said blocked illuminating light beam atan entrance pupil of said selected interchangeable telescope.
 38. Thesystem according to claim 36, wherein said apodizator isinterchangeable, and wherein said system further comprises additionalinterchangeable apodizators.
 39. The system according to claim 36,wherein said apodizator is dynamic, operative to block differentportions of said illuminating light beams.
 40. The system according toclaim 1, wherein at least one of said at least one light detector isdefined a multi-zone gray-field detector, said multi-zone gray-fielddetector comprising: a gray-field collector, divided into a plurality ofsections, each said sectors defining a detection zone; a plurality oflight detecting units; a plurality of light guides, wherein each saidlight guides optically couples one of said sections with one of saidlight detecting units, each said light detecting unit detecting at leasta portion of light directed thereto, by a respective one of said lightguides.
 41. The system according to claim 40, wherein at least one ofsaid light guides comprises an optic fiber.
 42. The system according toclaim 40, wherein at least one of said light guides comprises a specificshape molded transparent light guide.
 43. The system according to claim40, wherein at least one of said light guides comprises at least onemirror.
 44. The system according to claim 40, wherein said sectionsdivide said gray-field collector horizontally and vertically.
 45. Thesystem according to claim 40, wherein said sections comprise: at leastone horizontal section; at least one vertical section; at least onecircular section, spread across an area of said gray-field collectorbetween a selected one of said at least one vertical section and aselected one of said at least one horizontal section.
 46. The systemaccording to claim 40, wherein said sections comprise: a right section;a left section; a top section; a bottom section; a top-right section; abottom-right section; a top-left section; a bottom-left section; and acentral section.
 47. The system according to claim 40, wherein at leastone of said light detecting units is operative to detect light at atleast one predetermined wavelength.
 48. The system according to claim40, wherein at least one of said light detecting units is furthercoupled with an analysis system.
 49. The system according to claim 40,further comprising a relay lens assembly, located in front of saidgray-field collector.
 50. System for scanning a surface, comprising: alight source producing an illuminating light beam; an objective lensassembly, located between said light source and said surface; at leastone light detector; and an annular mirror located between said lightsource and said objective lens assembly, admitting said illuminatinglight beam and deflecting at least a portion of a reflected light beamreceived from said objective lens assembly toward at least one of saidat least one light detector.
 51. The system according to claim 50,further comprising a polarizing beam splitter, located between saidlight source and said annular mirror, admitting said illuminating lightbeam and deflecting at least a portion of said reflected light beamadmitted through said annular mirror toward at least another of said atleast one light detector.
 52. The system according to claim 50, whereinsaid at least one of said at least one light detector is a gray-fieldlight detector.
 53. The system according to claim 50, wherein said atleast other of said at least one light detector is a bright-field lightdetector.
 54. The system of claim 50, further comprising a quarter waveplate located between said polarizing beam splitter and said annularmirror, wherein said illuminating light beam is linearly polarizedbefore passing through said quarter wave plate.
 55. The system of claim50, wherein said at least portion of said reflected light beam,reflected by said annular mirror, is defined as a gray-field reflectedlight beam.
 56. The system of claim 50, wherein light reflected by saidannular mirror, is defined as a gray-field reflected light beam.
 57. Thesystem of claim 51, wherein light reflected by said polarizingbeam-splitter, is defined as a bright-field reflected light beam. 58.The system of claim 50, wherein the inner diameter of said annularmirror is in the order of the diameter of said illuminating light beam,right before passing through said annular mirror.
 59. The system ofclaim 51, wherein the deflecting plane of said polarizing beam splitteris limited to the order of the width of said at least a portion of saidreflected light beam admitted through said annular mirror, right beforebeing deflected by said polarizing beam splitter.
 60. The system ofclaim 50, further comprising a relay lens assembly located between saidannular mirror and said objective lens assembly.
 61. The system of claim50, wherein said light source produces said illuminating light beam, soas to scan said surface.
 62. The system of claim 50, further comprisinga plurality of interchangeable telescopes, a selected one of saidinterchangeable telescopes being located between said annular mirror andsaid objective lens assembly, adjacent to said objective lens assembly.63. The system of claim 62 further comprising a polarizing beam splitterlocated between said light source and said annular mirror, admittingsaid illuminating light beam and deflecting at least another portion ofsaid reflected light beam passing through said annular mirror, toward atleast another of said at least one light detector.
 64. The system ofclaim 50, wherein said light source produces said illuminating lightbeam, so as to scan said surface.
 65. The system of claim 50, whereinsaid surface is selected from the list consisting of: a wafer; a mask;printed material; and fabric.
 66. The system of claim 62, wherein saidobjective lens assembly is located at a fixed distance from saidsurface.
 67. The system of claim 50, wherein said objective lensassembly is located at a fixed distance from said surface, for eachselection of said interchangeable telescopes.
 68. The system of claim63, further comprising a quarter wave plate located between saidpolarizing beam splitter and said selected interchangeable telescope,wherein said illuminating light beam is linearly polarized beforepassing through said quarter wave plate.
 69. The system of claim 62,further comprising an interchanging mechanism, wherein at least selectedones of said interchangeable telescopes are located on saidinterchanging mechanism, interchanging to a selected telescope when oneis selected.
 70. The system of claim 69, wherein said interchangingmechanism is selected from the list consisting of: a turret; and aslide.
 71. The system of claim 50, further comprising an analysismodule, coupled to said at least one light detector.
 72. The system ofclaim 62, further including a teleconverter lens assembly, opticallyassociated with said selected interchangeable telescope.
 73. The systemof claim 72, wherein said teleconverter lens assembly is located betweensaid selected interchangeable telescope and said objective lensassembly.
 74. The system of claim 72, wherein said selectedinterchangeable telescope is located between said teleconverter lensassembly and said objective lens assembly.
 75. The system of claim 72,further comprising a controller coupled to said teleconverter lensassembly, wherein said controller operates said teleconverter lensassembly to adjust the combined magnification of said teleconverter lensassembly and said selected interchangeable telescope.
 76. The system ofclaim 75, further comprising an analysis module, coupled to said atleast one light detector and to said controller, wherein said analysismodule analyzes light readings provided from said at least one lightdetector, for the purpose of detecting defects, said analysis moduledetermining a new magnification level when detecting a suspected defect,and instructing said controller to operate said teleconverter lensassembly to adjust to said combined magnification to said newmagnification level.
 77. The system of claim 62, wherein at least one ofsaid interchangeable telescopes comprises a zoom telescope.
 78. Thesystem of claim 77, further comprising a controller coupled to said zoomtelescope, wherein said controller operates said zoom telescope toadjust the magnification of said zoom telescope.
 79. The system of claim78, further comprising an analysis module, coupled to said at least onelight detector and to said controller, wherein said analysis moduleanalyzes light readings provided from said at least one light detector,for the purpose of detecting defects, said analysis module determining anew magnification level when detecting a suspected defect, andinstructing said controller to operate said zoom telescope to adjust tosaid magnification to said new magnification level.
 80. The system ofclaim 50, further comprising: an apodizator located between said lightsource and said annular mirror; and a relay lens assembly locatedbetween said apodizator and said annular mirror.
 81. The systemaccording to claim 80, wherein said light source produces an image ofsaid illuminating light beam on said apodizator, wherein said apodizatorblocks at least a portion of said illuminating light beam, and whereinsaid relay lens assembly images said blocked illuminating light beam atan entrance pupil of said objective lens assembly.
 82. The systemaccording to claim 80, wherein said apodizator is interchangeable, andwherein said system further comprises additional interchangeableapodizators.
 83. The system according to claim 80, wherein saidapodizator is dynamic, operative to block different portions of saidilluminating light beams.
 84. The system according to claim 50, whereinat least one of said at least one light detector is defined a multi-zonegray-field detector, said multi-zone gray-field detector comprising: agray-field collector, divided into a plurality of sections, each saidsectors defining a detection zone; a plurality of light detecting units;a plurality of light guides, wherein each said light guides opticallycouples one of said sections with one of said light detecting units,each said light detecting unit detecting at least a portion of lightdirected thereto, by a respective one of said light guides.
 85. Thesystem according to claim 84, wherein at least one of said light guidescomprises an optic fiber.
 86. The system according to claim 84, whereinat least one of said light guides comprises a specific shape moldedtransparent light guide.
 87. The system according to claim 84, whereinat least one of said light guides comprises at least one mirror.
 88. Thesystem according to claim 84, wherein said sections divide saidgray-field collector horizontally and vertically.
 89. The systemaccording to claim 84, wherein said sections comprise: at least onehorizontal section; at least one vertical section; at least one circularsection, spread across an area of said gray-field collector between aselected one of said at least one vertical section and a selected one ofsaid at least one horizontal section.
 90. The system according to claim84, wherein said sections comprise: a right section; a left section; atop section; a bottom section; a top-right section; a bottom-rightsection; a top-left section; a bottom-left section; and a centralsection.
 91. The system according to claim 84, wherein at least one ofsaid light detecting units is operative to detect light at at least onepredetermined wavelength.
 92. The system according to claim 84, whereinat least one of said light detecting units is further coupled with ananalysis system.
 93. The system according to claim 84, furthercomprising a relay lens assembly, located in front of said gray-fieldcollector.
 94. Method for inspecting a surface, comprising theprocedures of: directing an illumination light beam through a selectedone of a plurality of telescopes and through an objective lens assembly;collecting a portion of a reflected or scattered light, at saidobjective lens assembly, said portion defined a reflected light beam;and directing said reflected light beam back through said selectedtelescope.
 95. The method according to claim 94, further comprising theprocedure of detecting at least a portion of said reflected light beam.96. The method according to claim 94, further comprising the procedureof directing said illuminating light beam through an apodizator and arelay lens assembly, thereby blocking at least a portion of saidilluminating light beam.
 97. The method according to claim 96, furthercomprising the procedure of directing at least a portion of saidreflected light beam toward a bright-field filter, thereby blocking atleast a portion of said reflected light beam from reaching a lightdetector.
 98. The method according to claim 94, further comprising: apreliminary procedure of directing said illuminating light beam througha polarizing beam splitter, a quarter wave plate and an annular mirror;and a procedure of directing a bright field portion of said reflectedlight beam through an aperture of said annular mirror and said quarterwave plate; a procedure of reflecting said bright-field portion by saidpolarizing beam splitter, toward a light detector; and a procedure ofreflecting a gray-field portion of said reflected light beam, by saidannular mirror toward another light detector.